Billion 7800 and Clarity DSL Surge Protector.

Been using a speedtouch 546 with a DSL surge protector from Clarity.it for eons. Got my Billion 7800 today and did the swap. No DSL signal. Light constantly flashing. So after a lot of head scratching removed surge protector on dsl line and bingo DSL sync. Anyone got any idea why a DSL surge protector would block one router and not another?

Is it to do with Inner/outer pairs on the RJ12?

Some routers work with either and others with just one. There could well be an incorrect swap over happening - or one which the Billion does not like.