Symptoms

When we open the SmartObject Tester tool and expand the "All SmartObjects" category, then the following error pops up:

The item name must be unique. 'ID' exists in the collection.

The same happens when we try to delete any workflow instance in Management Console.
 

Diagnoses

We wrote a SQL query to search for SmartObjects with duplicate entries in the SmartObjectXML column.

For more information, consult K2 Support and mention this number: 108013
 

Resolution

In the list of the results returned by the SQL query, we could spot the entry with the SMO GUID that looks a bit different than the rest. In the SmartObjectXML of this SMO we found, under the andltpropertiesandgt section, that there are two entries of andltproperty name="ID"andgt

Now we had two options:

1) Delete one of these entries in the XML
2) Delete the entire SmartObject in the database

We opted for option 2 since we saw that this SmartObject didn't exist anymore in the SmartObject Tester Tool. The category it was in did not exist anymore.

After deleting the SmartObject from the K2 database and restarting the K2 Service, everything was working again.