The UIAutomationCore.dll seems to be essestial for FSX and Windows 7 operating in 64 bits. Otherwise, you may be getting the same "Fatal Error" messages followed by a shutdown that is hurting a lot of other FSX users, as evidenced by numerous people like me reporting the problem in various forums on the web. One place where it may be downloaded is http://www.mediafire.com/?mik2mlqdz1w After saving it to your desktop or a folder, right click on extract all, extract the zip file, then using Windows Explorer drag the UIAutomationCore.dll into the main FSX directory. Apparently, FSX is a 32 bit program, and the UIAutomationCore.dll makes it work like a 32 bit program, thus preventing the fatal error messages that can come after serveral hours into an otherwise very satisfying fight. Moreover, for some users it speeds up their frame rates, and improves their display usage over dual monitor setups.
Thanks Charan Kumar for offering this solution!