Shortly before the summit attendees arrive through the Stargate, an announcement states that the base was finished being sealed off from the outside (for security). Yet immediately after this there is a shot of a group of soldiers running through the base with rifles, even though all weapons had to be removed from the base.
When the gate is dialing to bring the three Goa'uld to the summit, you can see that two stationary guns are still in the gate room even though there should have not been any weapons in the complex. Also, those guns are no longer present in the next scene.
When the three Gou'ald system lords are about to arrive through Earth's Stargate, the seventh chevron that locks (indicating the point-of-origin) during the incoming wormhole sequence is that of Earth, but the System Lords' point of origin was not Earth.