I had the same issue with gcc "gnat1" and it was due to the path being wrong. Gnat1 was on version 4.6 but I was executing version 4.8.1, which I had installed. As a temporary solution, I copied gnat1 from 4.6 and pasted under the 4.8.1 folder.
The path to gcc on my computer is /usr/lib/gcc/i686-linux-gnu/
You can find the path by using the find command:
find /usr -name "gnat1"
In your case you would look for cc1plus:
find /usr -name "cc1plus"
Of course, this is a quick solution and a more solid answer would be fixing the broken path.