Okay, I'm not sure what I did or changed (I don't *think* I changed anything ... ) but it started working again. I am running Windows 7 and, if this re-occurs, I will install WinDBG and capture the stack trace for you. I considered installing Qt4.3 and building from scratch so I could debug the issue myself but my last experience with Qt was less than stellar so I wanted to avoid that.
Thanks for the responses.
Macca