I recently stumbled upon this little bug by accident. If you create a folder called “Forms” in a document library, you won’t be able to re-name it or delete it directly. Backing up for a second, you can’t create a folder called “Forms” directly as a top-level folder in the library - the name conflicts with the hidden “Forms” folder that is inherit in any document library. However, SharePoint will allow you to create such a folder as a sub-folder to another folder.
Let’s say, for example, that you create a folder called “HR Documents,” inside which you create folders called “Policies,” “Procedures,” and “Forms.” If you try to delete or rename the “Forms” folder, SharePoint spits back an error message. This, apparently, is a known bug, but I have not come across a fix, as of yet.
The only way to rid yourself of such a folder is to delete the containing folder (e.g. “HR Document” in my example), or to delete the library altogether.
So, take heed in naming your folders.