odd Viewer & Canvas video after monitor calibration

I wonder whether anyone has answers for this oddity.

I calibrated my Dell Ultrasharp 2410 monitors using an iOne yesterday, got a reasonable balance with them both then opened FCP7 to an existing project that I've been working this past week or so. On opening FCP7 the images on the Canvas and Viewer windows were extremely dark, in fact nearly black when prior to the monitor they were absolutely normal. I closed the MacPro, re-started but it was the same. I had to junk the calibration to get the windows back to normal. The calibration I made wasn't radical at all, a slight shift in the blue and a small increase in brightness, almost infinitesimal, just bought both monitors close to each other which is what I needed.

Any ideas?

Thanks….