Damn,

I checked it once, while the engineer was there working on it and I didn't see anything out of place. The ip address and mask were definately correct but you've got me wondering about the gateway now, but I'm pretty sure it was ok. Problem is, it's a massive great steel plasma cutting machine for making bridges that you've got to shut down and restart to get to the config, and I dunno if I can remember how to do it. But I'll have a go. Any other ideas?

Not off the top of my head, but similar cases I've seen have always been invalid gateways.  Let me know how it works out for you.

do a self ping and see any odd route table by using the command route print / print route

Sounds like a pretty important machine.  Maybe there's an acl  that's blocking icmp traffic to the machine?  Try debugging icmp traffic to that machine - if you have access to the machine's first hop router you can run the debugs there and then send traffic. Normally when I try to single out a problemw w/ one device I'll run 'debu ip packet detail "acl" ' to keep from killing my router:

access-list 185 permit tcp host A host B

access-list 185 permit tcp host B host A

debug ip packet detail 185