Erroneous unknown symbol near top of file

I have intermittedly seen an unknown symbol error at the top of some of my files.  I haven't been able to figure out what causes this (maybe after I make changes to the file and commit them to my version control system using AnhkSVN?).  Deleting the first line in the (using System;) and this hitting undo immediately resolves the problem.  Very strange...

I'm using build 2163.