Remove interfering programs
Some programs on this PC may interfere with OneCare. To avoid performance problems on this PC, you should remove those programs.
I contacted OneCare support and got this reply that I have a hard time to understand. First SiteAdvisor is not an antivirus or firewall application and second OneCare does not provide what SiteAdvisor provides.
Please understand that any third party security software will conflict with Windows Live OneCare, so we recommend that removing the McAfee software to avoid conflicting with OneCare.Here is the reply I got from McAfee support:
When a computer has more than one Antivirus or Firewall application installed, the individual applications tend to conflict with each other for control of the computer's security. For example, with more than one Antivirus application running, every file on the computer that is accessed in any way is scanned by each individual antivirus application. Not only that, but all the files required to launch and perform the actual scanning operations are also scanned by the other applications, causing system performance issues and instability. This is sometimes referred to as an Antivirus Scanning Loop.
As Windows Live OneCare provides complete protection from viruses, worms, Internet attacks, and various other threats, we highly recommend uninstalling all other Firewall and Antivirus applications to avoid conflicts. If you have problems removing the third party applications please let me know and I will do my best to identify the contact information for the application's manufacturer to help you get in contact with them for further assistance.
McAfee SiteAdvisor is the 5-star rated Web safety tool that helps keep you safe from adware, spam and online scams as you search and browse the Web. McAfee products will not work with any other (third-party) Security software. Third party anti virus software from your computer may create a a conflict between the McAfee software which will cause incomplete or incorrect performance of your McAfee software.I wonder why not a word about this is told on SiteAdvisors page or in the FAQ.
SiteAdvisor is installed correctly and is working properly in your computer and is not interfering OneCare, If OneCare is creating conflict with McAfee you may decide, which security software to use.
Update: McAfee SiteAdvisor has now blogged about it.