I tried to update my McAfee DAT-files (Security Center 9.0, Virusscan 13.0) but after searching for an update for a long time, the software told me there were no updates available, although I knew there actually were, because my other computer did have a newer DAT-file. I tried lots of times, but always got the same result. No updates.
Then I tried to ask the McAfee Virtual Technician. It identified the problem and told me he could fix it for me. I let him, and it started the same update process as I had done lots of times before without any succes. But to my surprise, it worked. McAfee downloaded the new DAT-file and installed it.
Then after a few days, and one succesfull normal update, I had the same problem again! And again I asked McAfee Virtual Technician to fix it for me, and again it worked.
I don't know why it works, because the Virtual Technician does excactly the same thing as I do when I click on "Updates" in my McAfee software. And it's not a very easy solution when I have to do this every time, but it works.
I thought I should post the solution here. Perhaps it will help solve the problem for a while on your computers too...?