Recently, we did an upgrade for one of our client from SBS MSCRM 3.0 to 4.0.
Everything was going great and suddenly we got an error message
Action Microsoft.Crm.Setup.Server.MsiInstallServerAction failed.This patch package could not be opened. Verify that the patch package exists and that you can access it, or contact the application vendor to verify that this is a valid Windows Installer patch package.
Till this point we did not have any problem. After the error message CRM stops working. We did not find any component of MSCRM 4.0 installed.
We tried all sort of things but nothing worked. The problem was upgrade wizard could not find the installation package. It was looking for the package at some temporary internet files location.
The problem was caused by the update installation files step of the upgrade.
We tried to go ahead with the update without updating the files. It worked. We apply the the hotfixes after the installation.