Presumably the "Verify" failed because of the [DT Errors], whatever they are.
A verify is usually something like confirming what the PC thought it downloaded is the same as what is in the PLC.
Do you have another PLC-2 to which this program could be imported? If it works, then that isolates the problem i.e. the current PLC-2 (memory? I/O module? cable?) is suspect. Your "new program" suggests the PC and software are okay.
I'm not saying I have any experience with PLC-2, just follow the hints where they lead and try benign things to get more info; swapping a PLC might be a straightforward solution given your constraints; you don't need to know what the actual problem is, just how to get around it. If the customer does not have spares for summat this old, then this is what they deserve, and PLC-2 hardware can be found on eBay for a few hundred dollars, so that is at least as cheap as your time.