Error with plot_umap()

[grpinto]

I run plot_umap() on the augur object from calculate_auc() and on the sc_sim and I get this error :

plot_umap(augur,sc_sim)
Error in sc@reductions[[reduction]]@cell.embeddings :
no applicable method for @ applied to an object of class "NULL"

and then I actually try to apply UMAP and it does not work :

sc_sim <- RunUMAP(sc_sim, dims = 1:30, reduction = "pca", verbose = FALSE)
Error in slot(object = object, name = s) :
no slot of name "images" for this object of class "Seurat"

does somebody know how to fix this ?