I had a quick look at the Apache error log, but did not see anything relevant. But I only checked a portion of it, is this the place to look?
We have disabled the ERP integration to our system. And the error in the first post still occurs in *some* orders.
Is it possible to track down the SQL queries executed up to that error?
I am beginning to think that the problem lies in how some orders have been added in the database (perhaps in a slightly modified way) after the 3rd party software integration.
PS. Updated to latest VM 3.8.8, with no success in solving the issue.
EDIT: Forgot to mention in the first post... the problem only occurs when trying to change to a specific order status 'S'.
EDIT#2: I enabled Database Debug info, and it seems a 3rd party extension (which injects itself in product status updates) is to blame for this. First tests show the problem is resolved after disabling the extension.