We are using a peer to peer network and quickbooks premier 2011 is installed on all computers. The company file is stored on 1 computer and the file is shared for the others. This has been working fine since installing quickbooks 2011 over a year ago and earlier versions before that. All computers run NIS 2012. About 1-2 months ago, one of the computers started getting an error when trying to open Quickbooks. "Quickbooks has encountered a problem", and suggest running the Quickbooks connection diagnostic tool which we did. When we test the connectivity with the tool, the "IP reverse lookup status", "DB service status", and "port service status" all test ok. The only error we get says the company file directory is "not writable." We can disable Norton autoprotect on this computer only and everything works fine. About a week ago, another computer started doing the same thing. We can disable autoprotect on it and everything works as it should. We can ping the other computers and map the drive with autoprotect active, but still cannot log in to quickbooks unless autoprotect is disabled. We can enable it after logging in and no problems. We tried uninstalling Norton and everything works fine. When we reinstall Norton, we're back to the same problem. All the computers are running XP. All computers have the latest Windows updates and Norton updates. We're stumped!