Moving a folder copies it, no longer moves it
Do you have write permission to the parent folder of the folder? If you don't, you can force moving the folder by holding command while dragging it.

You can see if you have write permission to a folder by running ls -led /path/to/folder:

$ ls -led Desktop/untitled\ folder/
drwxr-xr-x+ 2 lauri  staff  68 Nov 21 08:46 Desktop/untitled folder/
 0: user:test allow list,add_file,search,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity



If the output includes lines for an ACL like above, try removing the ACL with sudo chmod -N /path/to/folder.
If the owner in the third column of the first line is not you, try running sudo chmod $USER /path/to/folder.
If the owner is you but you don't have write permission, or the first column looks like dr-xr-xr-x+ instead of drwxr-xr-x+, try running sudo chmod +w /path/to/folder.