Hi vsmall. I've no idea what causes this behaviour. When mysterious behaviour such as this occurs it is usually a damaged file (probably a dll file) somewhere in the operating system. Trying to find which file is damaged is almost impossible and reinstalling the operating system is usually the easiest solution.
If you occasionally post to this thread, you will keep pushing it to the top of the page, and hopefully someone will recognise the problem and be able to offer more useful advice than I can.