well, I'm thinking a couple of things you can do.
First, do you get the same problem if you try to compile a C program (i.e. directly with gcc, instead g++)?
Could you write what is the exact command you typed, and the output?
Did you try the '-v' (verbose) option?What does it say?
Have you checked if you have an executable output of the compiler in the same directory with the same name but whitout writting permissions? (maybe the compiler tries to overwrite the file and it cannot)
Or maybe you have a problem with the configuration of the compiler. Did it happen before, or is the first time?What did you change since the last time the g++ worked well?