If you are unable to rename or delete a file or folder it is possible it is already in use by another program. A program that uses something in a sub-folder can also lock the parent folder, so that it cannot be renamed or deleted. Which program has a particular file open is often not obvious, and it can be hard to figure out which program you need to close to be able to rename or delete the file or folder.
Under the Tools menu you can select "Find Opened/Locked Files" to find what program has a file/folder locked so that you can close or kill it. If you are running with standard user permission you will only be able to scan the system for processes that are running under your account: System & Service processes will not be found.
Running Multi Commander as an Administrator will allow you to also find Services and System processes that have files open or locked.