All the commands below are run from SmartSVN. We consider here files local status (not remote). Remember that svn add and svn remove must be completed by a svn commit to be validated on the server.
You tried to remove a file from svn and commit is not possible.
Check if you did svn remove on the directory in the Files lateral panel. If so, the svn commit must also be done directly on the directory (and not at the level of the files containaed in the directory).
May happen when a local remove has been processed and someone else removed / commited the file on the svn server.
Select file and choose mark resolved, option 1 (not 'accept incoming delete')
Revert will cancel your local action (remove, delete, move…) and may solve the problem.
Revert will cancel your local removing order and accept the commited modification by the other user, the file will become unchanged locally.