A possible reason is as follows:
There was a GlassButtons folder that was added to your local working copy (SVN Add) and subsequently removed from disk. This will lead to the situation you are facing: AnkhSVN is trying to commit this folder and therefore wants to read it from disk, but it no longer exists, so it gives this error.
The following should help you:
- Install TortoiseSVN
- ... \Helpers\Controls
- SVN
- GlassButtons. " " ""
- ""
.