As you know when doing any sort of Server migration like Small Business server it is always best practice to remove the ISA Server as it can cause problems with moving mailboxes.
When trying to move the mailbox you might get the following error.
MapiExceptionNetworkError: Unable to make connection to the server.
To resolve this you need to uninstall ISA and then try the move again. Problem is sometimes when trying to uninstall ISA you will get the following error:
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.
I have found 2 different solutions to resolving this problem:
1. Run the Microsoft’s Fix problems with programs that can’t be installed or uninstalled which can be found here:
When running you will select ISA from the list and even thou the Tool says that it could not repair ISA you will still be able to completely uninstall it.
Unfortunately this tool sometimes give the following error message when trying to run it on a Small Business Server.
This troubleshooter does not apply to your system
We’re sorry, but this troubleshooter is not compatible with your current system’s configuration.
2. What I did to get around this problem was download and install ISA 2004 Service Pack 3 from the link below and re-apply it. After that I was able to uninstall ISA completely.
Link to ISA SP3: http://www.microsoft.com/en-us/download/details.aspx?id=8836