Thanks for your post- I checked our bugtracker, and this kind of message has come up previously, although only very occasionally.
One user observed that they fixed it with the following process:
Problem occoured on an initial commit from my database to an empty source control location. I've figured it out - problem was caused by SVN settings located in %APPDATA%\\Subversion\\config file. 'enable-auto-props' setting was set to 'yes'. Changing it to 'no' solved my problem.
Could you maybe see if that helps in your case? We don't expose the actual setting anywhere (we use the SharpSVN library, which I believe should honour whatever is configured locally via Tortoise etc.)