Log-on Screen anomaly

I have a MacBookPro with OS 10.7.2. Every so often (perhaps five times in the past couple of months), on booting my laptop to the grey sign-on screen, there is on the right side a series of white lines about an inch wide (resolution 1344 X 840). I am able to log on in the normal manner, and the lines disappear when the desktop opens. Everything else works fine. I have put a JPG of the screen at http://www.eastbrookwind.org/screen.jpg Has anyone else experienced this? Thanks.

First thing I'd do is set it back to the native resolution of your MBP.

I have reset it to 1440 x 900.
Thank you.