I have an XPS420 with a single ATI 3870 graphics card an Vista Home Premium 32bit. I recently tried to upgrade my graphics card drivers and my ATI Catalyst Control Center. On advice from this forum downloaded the latest versions from the ATI website rather than from the Dell website. The Graphics drivers installed perfectly but when it tried to install Catalyst it displayed the following error message. "Could not load file or assembly 'MOM.Implementation, version=2.0.330.00.40205, culture=neutral, publickey token=90ba9c70ff846762e' or one of its dependencies. The system could not find the file specified." I rebooted my PC and when Windows loaded it displayed the folowing message "Could not load file or assembly 'CLI.Implementation, version=2.0.330.00.40205, culture=neutral, publickey token=90ba9c70ff846762e' or one of its dependencies. The system could not find the file specified." This message also displays whenever I try to manually run Catalyst. I remember from installing Catalyst on some older PCs that it requires Microsoft .Net to be installed, and the web suggests that this is a .Net error, but I already have .Net 3 installed. I upgraded to 3.5 rebooted, but it did not help, though I haven't yet had time to uninstall and reinstall Catalyst to see if it makes any different. There are some suggestions that this fault may also be caused by me having an older version of the Microsoft C++ libraries, but I don't know how to install/upgrade them, and I don't want to perform a complete system reinstall. Any ideas?