DateTime Format Exception when submitting a form

 I have a problem with a form where I have a Date-only field. When submitting it I get a DateFormat-exception.

 Been looking into the problem and found the following : The error occurs in AppForm.LoadFormSubmitData : crmFormSubmitXml, the message is othervise good but for the datefield I have the following tag <mff_txdate>0</mff_txdate>. This obviously doesn't translate into a date that well.

 I have CRM2011 Update Rollup 5 installed the behaviour is the same in Rollup 4. No manipulation is done on the field using javascript in any. Anybody seen anything like this?

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Kjel