My version is antivirus plus 2011.
When I run full scan or quick scan, a dialog says "an error has occurred". See attached screen shot.
Have any other security software installed on your computer like Microsoft Security Essentials, Paid Anti-Malwarebytes, Norton…etc. along with McAfee? Let us know the operating system with service pack and RAM size of your computer.
To your questions, I don't have any other software installed before (I just install MSE because McAfee doesn't work). Win7 64-bit SP1, 4GB. It worked before, but I don't realize when it failed.
I tried to find answers here. I saw quite a number of users have had the same problem for years, and they are asked to provide their system information, but I really don't see what's the matter. It is clear something wrong with McAfee software.
I also had some troubles install it when I bought it last Oct. I don't think I will use McAfee again when the current subscription expires.
Please remove all other security software including Microsoft Security Essentials and restart your computer. If you face the same issue after restarting the computer, remove McAfee from your computer and ran MCPR tool (http://download.mcafee.com/products/licensed/cust_support_patches/MCPR.exe), restart your computer and re-install McAfee.