data type mismatch - IMAGE object

[Brian Bennings]

We have a 4.5b system where we use archivelink functionality in a custom
workflow.  One of the initial steps of the workflow is to instantiate the IMAGE
object.
 
Recently, we have had 10 work items, all from the same day, that could not
execute this step in the workflow.  The message (WL 109) states the following:
 
"According to the container definition, expression references an object of type
u.  However, the element to which this expression is allocated is defined with
Dictionary reference IMAGE."
 
This is the only time we have known this to happen.  It has worked successfully
for thousands of other work items.
 
>> What is type "u"?
>> What could be causing this problem?
>> Do you have any tips on how to troubleshoot this further?
 
Thanks,
Brian