You must have a long path to the projects directory:
There is a maximum file name/path length etc inherent to each OS and VS has to respect that. The exact maximum character length for a filename is calcultated (up to an upper limit) and your solution parent folder path is part of it.
See
MSDN how a project max path and solution name length is calculated[
^] VS2010 might have a different way of working, but the principle will be the same.