PT 8 stopped working

[stereodesign]

I upgraded to PT 8 last week, everything went smoothly.
I used it on a session yesterday, again everything went smoothly.

Today I try to run PT and get the following error

"The application failed to initialize properly (0x80000003). Click on OK to terminate the application."

So I remove PT8 re-install, same problem.

I try removing PT 8 and re-installing PT7.4, same error.

A quick Google revealed someone who had this error in PT 8 LE and the replies were saying the only way to cure it was to re-install Windows, a somewhat drastic solution!

What has happened? Anyone else had this problem or know of a solution?