According to MacErrors.h, that error is a Core Foundation error
coreFoundationUnknownErr = -4960
That error file is located in /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/CarbonC ore.framework/Versions/A/Headers/.
You might have a corrupted system. Create a new admin user account, log into it, and see if the problem persists. If so, then it's system-wide and I suggest repairing permissioins. If that doesn't fix things, reinstall the latest COMBO update. If the problem doesn't pop up in the new account, then you've got problems within the original account.