I've had similar wierdness sometimes.

Problems are various - sometimes there is an identical file somewhere in your project, sometimes vs.net seems to be "thinking" about an older version of the file...  I generally just close and restart vs.net and it goes away.  if that doesnt work for u (in concert with an iisreset) try using vstweak and emptying vs.net's cache (i think it has an option for that)