" Wizard ended prematurely" - now what?

I tried to install FortiClient Standard 4.1 on a system with a known malware problem. It ended with the message " ...Setup Wizard ended prematurely because of an error" . I tried installing in Safe Mode but it wouldn' t. I repeated the process and got the same error. Anybody know what to do now? Or where in the KnowledgeBase to find information about this?