Workflow Error: "Object reference not set to an instance of an object."
When selecting a workflow in the MMC, the following error message is displayed:
Object reference not set to an instance of an object.
There is a version mismatch between the MMC you're using and the Administration Service you're connected to. Since version 7.x, there is no longer a version check when connecting across to other 7.x versions.
Upgrade your MMC to match the version of the Administration Service that you're connecting to.