I have a site which is experiencing the same exact error and maybe I can help clear up the issue by working with you.
The site version was 7.0.4, we wanted to upgrade to latest to resolve security issues. I downloaded the 7.4 Upgrade package, made sure the zip file was unblocked, extracted to a new folder, then copied all those new files over the existing ones.
After refreshing the page, so it would start the upgrade process automatically, I received the cannot find stored procedure dbo.AddException error. I checked with SSMS and that stored procedure is indeed not actually there.
I checked the EventLog:
SELECT TOP 1000 [LogTypeKey],[LogConfigID],[LogUserID],[LogUserName],[LogPortalID],[LogPortalName],[LogCreateDate],[LogServerName],[LogProperties]
FROM [DNN_BPC].[dbo].[EventLog]
ORDER BY [LogCreateDate] DESC
The last 3 logs are just Application_Start, the fourth was my last host login success 9 minutes before that.
I checked the Event Viewer, and there are no informational, warning or error messages in the last 20 minutes (when I attempted this upgrade).
That all said, do we know which SQL upgrade script might not be running on it's own? I can try downloading an interim upgrade such as 7.1, then 7.2, then 7.3 if necessary, though annoying.