Product Family: Act!
Product: Act! Pro, Act! Premium, Act! Premium (access via web)
Version/SP: Act! 2005 and later
Cause: This error will occur when there is more than one Act! user in the database that does not have a name listed under their Contact field.
Solution: To resolve this issue, you will need to add a name to the Contact field for every Act! user in the database. This issue can also result from two users who have the same Contact name in their contact record. You will need to change the name of one the records to make it unique.