My OS is win 7 prof 64 bit and I have office 2007 and also Avast Premier anti virus. The Outlook 2007 works erratically, sometimes it seems to load without any problems, but at other times it seems to be "not responding" for a very long time, and I have to use the Task manager to end the process. Avast is also protecting the emails and I am not sure if Avast is the culprit, and maybe if I should create an exception somewhere. I have done all the initial trouble shooting, running office's diagnostics program, then doing a scanpst on the pst files, and repairing them. But I skipped the OST files as I am not sure what it does and whether I should also scan these too. Hope the experts can please suggest how to fix this problem.