CRM 2013 Insufficient Form Permissions

We had some users who encountered a strange error in their upgraded CRM 2013 environment. We saw this happen on the account and contact form whereby the users were presented with an "insufficient permissions" error when they attempted to open the form.

The resolution proved elusive because the issue itself was very inconsistent. A little hard to explain or understand but the following example illustrates the type of behavior that was being experienced:

1. User experiences permission issue
2. Assign system administration role to user
3. User able to open forms
4. Remove system administration role from user
5. User still able to open forms
6. Later on user again experiences permission issue

So without changing anything the problem mysteriously goes away. Only to resurface at a later point in time (usually after logging out/in but not even that was consistent). So somehow this issue seemed to "cache".

This was despite the fact the user roles assigned did indeed have the necessary read permissions for these entities. And the users could in fact see the views for these entities but were blocked with the message above when trying to open any record.

The first thing to track down was to ensure that the users had permissions to the forms in question. After all, we had created a custom form to replace the built in version as part of the 2013 upgrade merge effort. But this also passed the test with the form being accessible to everyone (and enabled as fallback even though this was irrelevant since this was the only active Main form for the entity).

So this issue had to somehow be permissions related. After a bit of trial and error the issue seemed to hinge around the following "Process Configuration" read permission. This permission existed in CRM 2011 but for some reason (bug?) CRM 2013 is now requiring it to open these forms.