Blank grey Screen with Fireworks

I'm working on an older Mac Pro (2 x 2.4 GHZ Quad-Core Intel Xeon) , running OS 10.7.5. The graphics card is: AMD Radeon HD 7950, and was installed last year.

I've started working with Fireworks CS5 again, after a long hiatus. Right in the middle of an operation, the dialogue box goes blank and grey. I tried to reboot, but no luck.

Thank you for any thoughts you have on this!