Related to questions:
Is it possible for two gates to be simultaneously active on the same world?
In the Stargate SG-1 episode Touchstone, it is revealed that the N.I.D. were using the second gate around the same time S.G. one were using theirs. Yet in episodes such as Stargate SG-1's Watergate, Stargate Command is unable to dial out due to another active wormhole.