Hi Tony,
Sounds like your initial upgrade may have been incomplete, one possibility which may have caused the incomplete upgrade is a timeout.
Before reinstalling the Cart, try increasing the maxRequestLength, requestLengthDiskThreshold and executionTimeout values of the httpRuntime node in your application Web.config file.
I recommend using the instructions found in the following Article to perform a clean installation of the Cart. If you have a live site and need retain your customer, order and product data before doing a clean installation please see the pdf attached to the Article which explains how to export and import so you can retain your data when doing a clean installation:
https://www.smith-consulting.com/Foru...
Thanks,