When deleting a folder you might get an Error 41 saying it cannot be deleted, this usually means it’s not empty even though it appears to be empty in ProjectWise Explorer.

Cannot delete a folder in ProjectWise Explorer 'Error 41'

Please add a folder id column in the view you have (under view choose columns…/folder columns->folder id)

Then it should show the number of the folder that you are having trouble with in this columns, please go to your server's storage location and check this folder out, you will most likely find at least one file that was left there.