I have a form that contains an iFrame of the Web Client. In the Web Client, I have a custom tab that allows me to submit another form (formsception?). 

If I submit the form that is in the Web Client, and then submit the main form, I get the following error:

Refreshing the screen and resubmitting works fine. But if I submit the form in the custom tab before submitting the main form, I get the same error.

Any ideas? Preferably a workaround that will allow me to keep the current set up?