Practice Management: Error: 'An unexpected error has occurred and the console will exit... invoke or BeginInvoke cannot be called on a control until the window handle has been called' occurs when opening/previewing an invoice

This problem often occurs when the user accidentally closes the "Rich Text Form" that usually appears in the background when we print or email an invoice for the first time.
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If the user has closed this window, they will face this error when trying to preview any future invoices.
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To fix this, the user will need to completely log out of APS and then log back in.