Trouble checking in files using Tortoise-SVN

I had this problem today, where I could not check-in my modified files to SVN, the message I got was:

I tried all sorts of fixes (update, cleanup commands, etc) and googled it too, in the end I decided the brute force attack was the only way to go so I copied the modified files to another location, deleted the local folder from my hard drive, updated the parent folder from SVN, which restored the troublesome folder then copied the modified files back, ran the commit and hey presto, fixed.