Dynamics 365 8.2 to 9.1 Upgrade
During the process of upgrading from Dynamics 8.2 to 9.1 we encountered plugins that worked in 8.2 but caused errors when trying to browse CRM in the upgraded 9.1 environment.
We had assistance from Microsoft in troubleshooting the problem, but there was an issue where it was found that it was a Sandbox Execution Error, but there was no detailed exception message. We also had a clue that the error was from a plugin that ran as soon as CRM was opened. So we choose to unregister three of the Independent Software Vendor plugins, and then we were able to browse CRM.
Note that the upgrade from 8.2 to 9.1 is a double-upgrade, in that you need to first upgrade to 9.0, and then 9.1. After un-registering the plug-ins in version 9.1, we went back to 9.0 and removed just two of the three plug-ins that were no longer needed, prior to the upgrade to version 9.1
In order to locate the Plug-in Registration Tool, we referenced this blog article: download the Dynamics 365 plugin registration tool.