SAP Note 14819 - Sales activity overview: customer number is gone

Symptom:

When you enter a sales activity, the customer number is displayed on the overview screen. If you then exit the overview screen (goto other sales activity screens or save sales activity) and then call the screen again, the customer number is gone.

Cause and prerequisites

Handling error in Customizing.
(We suspect that error message E062 was issued during entry of the sales activity, this means that the customer has an account group for which the role AG (corporation) is not assigned. To enable entry to continue, the partner determination procedure was changed).

Solution
In the partner determination procedure corresponding to the sales activity type, add role AG as a required role again.