Troubleshooting internet connection issues, firewall settings, and having mulitple instances of QuickBooks installed on the computer.
QuickBooks runs the Verify Data utility as part of the normal backup process. If problems are found, you'll need to follow the provided instructions to rebuild your company data file.
Main list of links for update errors, including errors 1601; 1603; 15212; 15250; "The company file was not upgraded to match the version of the current server"; 1334, 1335, or 1336; and more.
Steps to resolve "Error 1335: "The cabinet file [data1.cab] required for this installation is corrupt and cannot be used."