This project must be converted to the current visual C++ project format

I'm getting the following error when I try to open my project using Visual Studio 2010.

This project must be converted to the current visual C++ project format

It has been working previously and Visual Studio works with other projects.

The only thing I can think of is that I may have tried to open it with an old Parallel Studio XE2011 with VS 2008.

Any suggestions on how I can open my project.

THanks