I have also have a DIR-625 with similar symptims. It is Rev A2, came with v1.09 F/W. I experience sporadic connection drops from a DWA-142. Most of the time things are great, and then suddenly the DWA-142 gets dropped and cannot get back on the network. I can see it connect, hold the connection for a few seconds, then terminate. It repeats the cycle forever.
Re-Starting the laptop with the DWA-142 has no effect; rebooting the DIR-625 has no effect, and even poering down the DIR-625 for a few minutes has no effect.
So far my only "fix" has been to shut down down all computers on the network, power down the router, and bring everything back up.
/SamCal/