X shut down compulsorily

I have a problem recently. It is forcing suddenly to terminate, while using X. Although I was looking to a problem solution sake at log file in order, I did not know after all where a cause was. The following is a part of XFree86.0.log when X falls. Fatal server error: Caught signal 11. Server aborting This phenomenon was generated no less than 3 times within the past two weeks. It did not generate before. This has been a very serious problem, in order to end suddenly during work by X. I am using SUSE 9.1 Pro on Opteron 246 * 2. Aren't there those who know this cause? Thanks, eshsf