Unable to update a pre-priced sales order from a third-party system

Summary:

I am attempting to update a pre-priced sales order from a third party system. When I safe the changes, I get an error.

Content (please ensure you mask any confidential information):

The error received is:

You can't save this draft order: You cannot edit this sales order line because you cannot modify the price, the tax, or the shipping charge. You cannot edit this sales order line because it resides in a sales order that was created in a different source system. You cannot edit this sales order line because it resides in a sales order that was created in a different source system. Source Order Information: 3004242-1-3397364-1. (FOM-4515069)