diff --git a/migrations/Migration.php b/migrations/Migration.php
index b7fa2458e..d8bd512f7 100644
--- a/migrations/Migration.php
+++ b/migrations/Migration.php
@@ -25,7 +25,7 @@ class Migration extends \yii\db\Migration
     protected $restrict = 'RESTRICT';
     protected $cascade = 'CASCADE';
     protected $dbType;
-    
+
 
     /**
      * @inheritdoc
@@ -54,22 +54,74 @@ public function init()
                 throw new \RuntimeException('Your database is not supported!');
         }
     }
-    
+
+    public function dropTable($table)
+    {
+        if ($this->dbType == 'sqlsrv') {
+            $this->dropTableConstraints($table);
+        }
+        return parent::dropTable($table);
+    }
+
+    public function dropColumn($table, $column)
+    {
+        if ($this->dbType == 'sqlsrv') {
+            $this->dropColumnConstraints($table, $column);
+        }
+        return parent::dropColumn($table, $column);
+    }
+
+    /*
+     *  Drops contratints and Indexes referencind a Table Column
+     */
     public function dropColumnConstraints($table, $column)
     {
         $table = $this->db->schema->getRawTableName($table);
         $cmd = $this->db->createCommand('SELECT name FROM sys.default_constraints
-                                WHERE parent_object_id = object_id(:table)
+                                WHERE parent_object_id = object_id(:table_1)
                                 AND type = \'D\' AND parent_column_id = (
-                                    SELECT column_id 
-                                    FROM sys.columns 
-                                    WHERE object_id = object_id(:table)
-                                    and name = :column
-                                )', [ ':table' => $table, ':column' => $column ]);
-                                
+                                    SELECT column_id
+                                    FROM sys.columns
+                                    WHERE object_id = object_id(:table_2)
+                                          AND name = :column
+                                )', [ ':table_1' => $table, ':table_2' => $table, ':column' => $column ]);
+
         $constraints = $cmd->queryAll();
         foreach ($constraints as $c) {
             $this->execute('ALTER TABLE '.$this->db->quoteTableName($table).' DROP CONSTRAINT '.$this->db->quoteColumnName($c['name']));
         }
+
+        // checking for indexes
+        $cmd = Yii::$app->db->createCommand('SELECT ind.name FROM sys.indexes ind
+                                                INNER JOIN sys.index_columns ic
+                                                    ON  ind.object_id = ic.object_id and ind.index_id = ic.index_id
+                                                INNER JOIN sys.columns col
+                                                    ON ic.object_id = col.object_id and ic.column_id = col.column_id
+                                                WHERE ind.object_id = object_id(:table)
+                                                AND col.name = :column',
+                                [ ':table' => $table, ':column' => $column ]);
+
+        $indexes = $cmd->queryAll();
+        foreach ($indexes as $i) {
+            $this->dropIndex($i['name'],$table);
+        }
+    }
+
+    /*
+     *  Drops contratints referencing the Table
+     */
+    public function dropTableConstraints($table)
+    {
+        $table = Yii::$app->db->schema->getRawTableName($table);
+        $cmd = Yii::$app->db->createCommand('SELECT name, OBJECT_NAME(parent_object_id) as tbl FROM sys.foreign_keys
+                                WHERE referenced_object_id = object_id(:table)',
+                                [ ':table' => $table ]);
+        $constraints = $cmd->queryAll();
+        foreach ($constraints as $c) {
+            echo 'Dropping constrain: '.$c['name']."\n";
+            $this->execute('ALTER TABLE '.Yii::$app->db->quoteTableName($c['tbl']).' DROP CONSTRAINT '.Yii::$app->db->quoteColumnName($c['name']));
+        }
+
     }
+
 }
diff --git a/migrations/m140504_113157_update_tables.php b/migrations/m140504_113157_update_tables.php
index 89c05cfa7..eae8d911a 100644
--- a/migrations/m140504_113157_update_tables.php
+++ b/migrations/m140504_113157_update_tables.php
@@ -53,6 +53,6 @@ public function down()
         $this->addColumn('{{%user}}', 'confirmation_sent_at', $this->integer());
         $this->addColumn('{{%user}}', 'confirmation_token', $this->string(32));
         $this->createIndex('{{%user_confirmation}}', '{{%user}}', 'id, confirmation_token', true);
-        $this->createIndex('{{%user_recovery}', '{{%user}}', 'id, recovery_token', true);
+        $this->createIndex('{{%user_recovery}}', '{{%user}}', 'id, recovery_token', true);
     }
 }
diff --git a/migrations/m140830_171933_fix_ip_field.php b/migrations/m140830_171933_fix_ip_field.php
index 76d1b6c04..87af8f5db 100644
--- a/migrations/m140830_171933_fix_ip_field.php
+++ b/migrations/m140830_171933_fix_ip_field.php
@@ -18,6 +18,10 @@ class m140830_171933_fix_ip_field extends Migration
 {
     public function up()
     {
+        if ($this->dbType == 'sqlsrv') {
+            // this is needed because we need to drop the constraint SQL created when renaming the column (?)
+            $this->dropColumnConstraints('{{%user}}','registration_ip');
+        }
         $this->alterColumn('{{%user}}', 'registration_ip', $this->bigInteger());
     }
 
diff --git a/migrations/m150623_212711_fix_username_notnull.php b/migrations/m150623_212711_fix_username_notnull.php
index 46afa50f1..1e69dc350 100644
--- a/migrations/m150623_212711_fix_username_notnull.php
+++ b/migrations/m150623_212711_fix_username_notnull.php
@@ -36,7 +36,7 @@ public function down()
             if ($this->dbType == 'sqlsrv') {
                 $this->dropIndex('{{%user_unique_username}}', '{{%user}}');
             }
-            $this->alterColumn('{{%user}}', 'username', $this->string(255)->null());
+            $this->alterColumn('{{%user}}', 'username', $this->string(255). ' NULL');
             if ($this->dbType == 'sqlsrv') {
                 $this->createIndex('{{%user_unique_username}}', '{{%user}}', 'username', true);
             }
diff --git a/models/UserSearch.php b/models/UserSearch.php
index cf0c18ffb..6a2a75e8a 100644
--- a/models/UserSearch.php
+++ b/models/UserSearch.php
@@ -103,7 +103,8 @@ public function search($params)
             $query->andFilterWhere(['item_name' => $this->auth_item]);
         }
 
-        $table_name = $query->modelClass::tableName();
+        $model = $query->modelClass;
+        $table_name = $model::tableName();
 
         if ($this->created_at !== null) {
             $date = strtotime($this->created_at);
diff --git a/views/admin/index.php b/views/admin/index.php
index 4ae2e1855..bdc2384c6 100644
--- a/views/admin/index.php
+++ b/views/admin/index.php
@@ -139,7 +139,7 @@
                     }
                 },
                 'switch' => function ($url, $model) {
-                    if($model->isAdmin && $model->id != Yii::$app->user->id && Yii::$app->getModule('user')->enableImpersonateUser) {
+                    if(!$model->isAdmin && $model->id != Yii::$app->user->id && Yii::$app->getModule('user')->enableImpersonateUser) {
                         return Html::a('<span class="glyphicon glyphicon-user"></span>', ['/user/admin/switch', 'id' => $model->id], [
                             'title' => Yii::t('user', 'Become this user'),
                             'data-confirm' => Yii::t('user', 'Are you sure you want to switch to this user for the rest of this Session?'),