Technically there's no limit.  But practice is another thing.  How many are you attempting?

I hesitate to admit this, because I am astonished that we can process anywhere near this many.

Using Tairox Productivity tools, Invoice Shipments customer has created (and processed) a number of invoices with over 10,000 lines.  The largest is from 1168 shipments and has 22,698 lines.

We are trying to create an invoice from 1,972 shipments which would have 37,713 lines and it is failing with "record has been altered by another program".  I assume this message is not actually the cause of the problem, as we have run several times, including after all other users have logged out, and it always fails at the same point.

I hesitate to admit this, because I am astonished that we can process anywhere near this many.

Using Tairox Productivity tools, Invoice Shipments customer has created (and processed) a number of invoices with over 10,000 lines.  The largest is from 1168 shipments and has 22,698 lines.

We are trying to create an invoice from 1,972 shipments which would have 37,713 lines and it is failing with "record has been altered by another program".  I assume this message is not actually the cause of the problem, as we have run several times, including after all other users have logged out, and it always fails at the same point.

Well, the "record has been modified" error can be caused by bad data, but figuring it out could be a nightmare.  Running RVSPY on a transaction that big could take days.   I think you need to do an A and a B invoice.