I know a number of so called experts will say it is crap software as it distributed by Microsoft but it actaully does work. I am a lan manager for my work and we run it all computers along with Corporate Edition anti-virus (the best Anti-Virus without question)...and although is it beta software it does find some malware that Ad-aware seems to miss - why who knows.
Perhaps if you can send us screen shot of yr error it might help. If you do not how to do a screen capture then let me know.