There is a bug on Windows 7 (and Windows Server 2008 R2) that relates to corrupted files error messages and affects several SVN’s operations (like commit and update). The detailed error message you can get is something similar to:
svn: Can't move '[repo]\.svn\tmp\entries' to '[repo]\.svn\entries': The file or directory is corrupted and unreadable.
And you can even get a Windows error message telling you about a corrupted file.
As I found in here and here, there is nothing to be afraid of, it is just another bug/error on Windows that is going to be fixed on SP1 (but there is already a hotfix ready to install). I haven’t finished test it myself (just missing the restart after the hotfix installation).
The hotfix’s download requires you to give your email address to Microsoft before they send you the link where you can download it (some way annoying). I have uploaded on my own server to avoid the process if I need it again, so you can get it from here if you want (remember that you should NOT download executables from non-trusted sources as they can contain viruses and harm your computer).