VS C#: Prompts me to resave, then refuses to open the file

Sometimes when I hit Save (ctrl+s) or just Save All, Visual Studio C# prompts me to resave the file I edited last. I can't save it as it is, because it already exists (and it should), and if I save it as something else, VS will prompt me for the file everytime I try to build.

If I shut down Visual Studio and try to access the file with notepad, it gives me an "access denied" message.开发者_StackOverflow中文版

This is starting to piss me off since I have to redo a lot of things. Any known cause?

I'm using Windows Vista (32-bit and logged in from an administrator account).

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Something is messing with the file, not Visual Studio. Use SysInternals' Handle utility to find out what process does this. Pop the network cable to block out co-workers with an odd sense of humor.