Symptoms
Mail block is not displayed in the communication panel. The console displays the following error message: Uncaught Terrasoft.ItemNotFoundException: Column with the '4684d4ba-4b6b-4d1a-93fb-70ec2afed57f' Id not found in the 'Activity' object
Cause
The EntityConnection table contains connection of an activity with nonexisting or outdated object.
Solution
Execute the following in the configuration or DBMS script, that deletes link to nonexisting column:
DELETE FROM [dbo].[EntityConnection]
WHERE [ColumnUId] = '4684d4ba-4b6b-4d1a-93fb-70ec2afed57f'
Necessary conditions and possible restrictions
Before executing, make sure that no column with such UId exists in the Activity object. It might be contained in one of the packages, but bpm'online may not see it due to the incorrect package dependancy.