Every so often, a document sent to the printer will reset the router, which results in a printer error.
Is there anyway to cure this???

Same with my Epson r300. Only cure is to unplug it from the router
This has been the same with all firmware revisions I've tried.

Yeah, its a real pain this. Set the printer printing a 70 page document and it printed pages 1, 2, 3 and four, reset then did the same about 20 times. Wasted a massive amount of ink, paper and my time.
I bought a draytek because thet are supposed to be the best.
Bought an epson printer for the same reasons.
Come on draytek, sort this!!!