This is presumably because the overall XPage compilation process isn't synchronized, and so one page may compile a CC that another page is working on, and then the ClassLoader instances become polluted.
[err] Caused by:
[err] java.lang.LinkageError: xsp.FieldReports_005fdailyDiaries_005fdeliveries
[err] at java.lang.ClassLoader.defineClassImpl(Native Method)
[err] at java.lang.ClassLoader.defineClassInternal(ClassLoader.java:391)
[err] at java.lang.ClassLoader.defineClass(ClassLoader.java:360)
[err] at java.lang.ClassLoader.defineClass(ClassLoader.java:315)
[err] at com.ibm.xsp.extlib.javacompiler.impl.SingletonClassLoader.defineClass(SingletonClassLoader.java:19)
[err] at com.ibm.xsp.extlib.javacompiler.JavaSourceClassLoader.findClass(JavaSourceClassLoader.java:157)
[err] at java.lang.ClassLoader.loadClassHelper(ClassLoader.java:946)
[err] at java.lang.ClassLoader.loadClass(ClassLoader.java:891)
[err] at java.lang.ClassLoader.loadClass(ClassLoader.java:874)
[err] at com.ibm.xsp.extlib.javacompiler.JavaSourceClassLoader.addClasses(JavaSourceClassLoader.java:244)
[err] ... 139 more
This is presumably because the overall XPage compilation process isn't synchronized, and so one page may compile a CC that another page is working on, and then the ClassLoader instances become polluted.