Dynamics NAV - LS Retail POS - Pharmacy - "POS Prescription Order Posting already exists."

Cause:
This happens when a prescription has had lines against it in the POS, but is then deleted or removed at the store level.
This results in orphan lines with references to a prescription that does not exist, and causes the POS to crash when attempting to exit the prescription from the POS.

Resolution:
Update the POS Trans. Line table, remove any references to the offending Prescriptions in the Prescription Order no. column.
Once removed, you will be able to void the pos lines as regular transactions.

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  update [CRONUS].[dbo].[CRONUS$POS Trans_ Line]
  set [Prescription Order No_] = ''
  where [Prescription Order No_] = 'PRPO095043'
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