I installed Microsoft Security Essentials on Windows XP professional and on Windows XP Media Center 64. On both machines, the compression agent will no longer compress large numbers of files. If I select 150 files, it starts working and then returns "Cannot create output file". If an atttempt is made to add a large number (150)of files to an existing archive, it adds 49 of the files, gives the error message, destroys the file name of the existing archive, replaces it with something like "BKa02120" and removes the file extention. It will create a new archive if I select 125 files but not 155. The files are tiny, 1k up to 40k.Both machines began the identical behavior after I removed McAfee and installed Security Essentials. I did use the McAfee removal tool on both, and had to pay Microsoft for a tech encounter to correct a problem on the 32-bit machine which prevented installation initially.1 person needs an answerI do too