If you get an error that says, "Sorry, you are not permitted to perform this action when trying to submit a design request" check that you are the assigned sales rep on the deal. The assigned sales rep is listed in the top right corner of the deal page, or at the top of the lead page.
If the user submitting the request does not match the assignee, this error may show.
A user with admin permissions can reassign the deal to clear the error, if needed.