I have this problem too. It started when I installed avast. I had this error for some time and then(I didn't do anything - as I know) it disapeard. It'd worked fine for some time and then again. I re-installed, changed the "Database" key of "data\avast4.ini" file from "ODBC" to "XML",
checked the Windows event log and there is a lot of errors, ashServ.exe is not in the process list, I have the latest version, in the avast log viewer there are 4 errors - one of them is - During the parsing of C:........DATA\avast4.xml XML document, following error occurred: C., I had some antivirus programs before but i uninstalled them correctly I think. I have ad-aware 6 an zone alarm installed. What's wrong?