So I am not sure what change would have caused this, but I think there is some built in pre-requisite that is broken.

When I attempt to change the product associated with a CRM Case, I get this JavaScript error:

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Message from webpage
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There was an error with this field's customized event.

Field:productid

Event:onchange

Error:Unable to get property 'AddParam' of undefined or null reference
---------------------------
OK  
---------------------------

I believe this to be caused by some change to the form that I made, generally this would be caused by a custom on change event, but I think it is something built in to system.  I found this JS in the incident_main_system_library.js, and it looks like it has something to do with entitlements.

Mscrm.productid_onchange=function(){if(Xrm.Page.context.client.getClient()!=Xrm.ClientNames.mobile){var oLookup=Mscrm.FormControlInputBehavior.GetBehavior("entitlementid_i");oLookup.AddParam("productid","")}};

Thanks for any assistance with this.