I'm using visual C++ 2010 express. I've had this happen a few times where I step away for a short amount of time, I come back and I can no long build a solution. Now I'm still very new to the program/language so I could have and more then likely did make a mistake to which the program is no longer able to preform the command. Could I be right in this case?
Did you build the program, run it, make some changes and then tried to rebuild? If so, it may be you haven't stopped the first program from running. Since it's still in memory, it can't be overwritten by the new program using the same name. Happens to me quite often. If that's not the case, you got me... Sorry..