Nobody can reply with any precise technical hypothesis if you limit yourself to such a very general and vague description.
I have been playing that game since the June 2007 beta version, and I have never experienced what you describe.
My hypothesis is that there is something problematical within your computer, but since you give no technical info whatsoever concerning your machine and in what program environment* it is trying to run the game, it is impossible to answer you.
* By "program environment", I refer to such things, for example, as : Do you run background programs (such as an antivirus) that might interfere with the game program? Do you regularly scan and clean your computer to free it of malware (viruses, trojans, adware, spyware, etc.)?