I have had this exact same issue ad searched the i-net but found no solution other than to completely uninstall AVG using AVG's Uninstaller and then use an application to search for any remaining traces of AVG and remove those too before re-installing AVG.
Instead of that, I went to Docs and Settings-> All Users-> Application Data-> AVG 0913b Campaign and deleted both the MachineIDCreator.exe and avguidx.dll components. I then did a thorough scan and AVG picked up 32 "medium threats" that it had failed to pick up before. After a reboot, I've had no further issues.
I am no expert here and I am not saying that this is the definitive solution to this issue, but it seems to have worked for me. If I were to guess, I would say that a virus had deliberately corrupted those two files.
To the mods/expert: if my post above is full of the proverbial and/or you have a better solution, please feel free to remove it. Cheers.