I've been playing with this one.
I started with a clean install of 5.6.8 and did an upgrade to 7.2.2. I get this message:
Application Error 07.02.02 Error!
After the upgrade the site seems to work normally.
If, however, I upgrade from 5.6.8 to 7.1.2 and then from 7.1.2 to 7.2.2, the upgrade proceeds without an error.
I'm not quite sure how to track down that "Application Error." Any pointers?
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A partial answer is to look in this file: /portals/_default/Logs/InstallerLog201458.resources
05/08/2014 13:05:27 [ERROR] DotNetNuke.Services.Upgrade.Upgrade Error: Object reference not set to an instance of an object.
at DotNetNuke.Services.Upgrade.Upgrade.MakeModulePremium(String moduleName)
at DotNetNuke.Services.Upgrade.Upgrade.UpgradeToVersion722()
at DotNetNuke.Services.Upgrade.Upgrade.UpgradeApplication(String providerPath, Version version, Boolean writeFeedback)
Is this an error in the upgrade routine? Or something else?