After updating a server to Plesk for windows 7.5.1, the webalizer program was not working anymore, even if it was installed, Plesk still reported as uninstalled. After two days of headaches, I found the cause of this problem. Basically, when I updated Plesk, I also updated the ClamAV antivirus to the latest clamav-devel codebase (0.83-8h) from http://www.sosdg.org/clamav-win32/index.php, I always used clamav versions provided there with success. The problem is due to an updated cygwin1.dll version (1005.14.0.0) that ships with the latest clamav version, while the cygwin1.dll provided in the webalizer directory is still 1005.12.0.0. Plesk launches webalizer under the same user So when Plesk launches "webalizer -V" to get program version, it receive a **shared memory mismatch** error and statsmng.exe doesn't receive the correct version string so disables it. I took a lot of time finding this because launching "webalizer -V" by hand as Administrator user works correctly even when ClamAV is running. But Plesk launches webalizer as the same user under which ClamAV is running so the two dll conflicts. The solution was to update the cygwin1.dll in the webalizer directory with the newest version from clamav.