Cannot remove non-empty dir with rm -rf

I try to remove directories that contain files in the command line by using rm -rf dir1. However,I receive error message telling

rm: cannot remove 'dir1': Directory not empty

Any ideas how to solve?


found the solution. A file called fuse_hidden produced the issues. I wasn't able to delete that file, even in not by rightclicking and deleting.

I used lsof dir/fuse_hidden to show processes using this file and closed them. After that I rm -rf was possible.