Form corruption on some workstations

We have developed an interactive form for users to enter offline and submit via email. We are preparing to move this into production, but we found that some workstations create forms that will not process correctly in the SMTP (email) function.

When a form is completed and sent via Outlook ( we use a submit button on the form) the email is returned with the error 554 ERROR_MESSAGE_STATE: USAGE ERROR

There is no short dump or SM21 log of this. The trace details show that the icm likely does not recognize the content correctly as pdf. It never makes the call to ADS. The workflow trace (and ST01) do not show that the user exit is called. We though that this might be the uuencode setting in Outlook, but it is not the cause.

Anyone else have this issue?