I have managed to solve the issue in the most bizarre way...
I currently use a draytek vigor2600g adsl/wifi router. I have read on the draytek forum of a few people suffering with other wifi connected kit. To this end I invested in a second wireless hub to replace the built-in draytek wifi. Both the netx and ipronto conencted up to the new hub and initially, the iPronto cerytainly seemed to be able to access the web much quicker so suggested that the new linksys hub was more performant. However, it could not see the NetX!! After restarting, changing ip's and everything else i could think of i decided as a last thought to connect the NetX via the draytek wireless connection and the iPronto itself via the linksys hub.
Incredibly it has been 100% reliable ever since!!
Not sure the message here but looking at the number of wifi related problems here I think it is pretty safe to say that wifi is not quite ready to replace good old cable yet!!!
