Strange behaviour for one specific user

Hi,
I have a rather frustrating problem.
I am working with a workflow, where invoices come in as XML files. The values in the XML file is entered into a temporary table, then validated, and last Navision invoices are created from these data.
It works perfectly fine... for me, my collegues, etc.

Only one person reports to have a problem with the posting date being modified, somewhere in the process of creating the invoices. The posting date is set to 25-04-2007, instead of the posting date in the temporary table. But this problem occurs only for this one person.

All users access the Navision database through Citrix Program Neighborhood.

Even though the zup-file shouldn't be the cause of this problem, I have tried to log-on using her username and password. The zup-file is centrally stored, so I must have been using the same zup-file as she has, even though we tried from different workstations.
I didn't have any problems. She still has.

I have no clue what can be wrong. The code is good and there are no user-specific conditions.

Can you help me here?

Yours sincerely
Emerik