Security Scan Plus is not protection software but merely a scanner that installs optionally along with 3rd party software such as Adobe products and all it does is tell you what protection you need. You can uninstall it from Control Panel/Add or Remove Programs (XP) Programs/Uninstall a Program (Vista/Windows 7).
You must have overlooked the option when downloading that software. It's not a McAfee problem, sorry.
You say you are using Avira...so what other McAfee software do you have installed? You shouldn't have 2 antiviruses installed at once.
If you want to activate other McAfee software the Avira is probably preventing that.