I believe we have finally worked out the problem AND the solution,
The Intel Proset software is at fault with only particular routers and when the notebook is low on power.
This is why its been a pain to resolve - most routers are OK.
The Proset software will conflict with, in our case, Windows 8.1 and glitches in the Proset registry section. This conflict is permanent if you attach to the offending router making Proset unaware of the WiFi card.
Solution
Repair the proset tool (by going in to control panel/programs and features - and hit repair when the proset program is selected) and THEN update to the latest version, 17 in our case - Repairing first is the critical part.
This may not work for everyone - BUT I have been dealing with this issue for the past year and have FINALLY got it resolved.
PS the offending Router is from iinet Australia - and is called a BOB.