I assume you can still unlock everything the old fashioned way, so there shouldn't be any issue with being "locked out".
Has this issue always been evident, or did the locks work properly initially and just recently stop working? I can't say this with 100% certainty, but I'm fairly certain the system doesn't use separate fuses for lock and unlock functions. However, it's not that hard to check all the fuses so that might still be a good place to start looking. A more likely scenario might be the power lock relays, of which there are two, one for unlock and one for lock. Both relays are the same part number, try swapping them and see if the problem changes from the unlock function to the lock function. It's a simple first or second step in diagnosing the problem.
Since the lights flash when you press the button, obviously the module is receiving the signal. Since the lock function works, obviously the module works for that function. If the relay isn't the problem, I'd suspect a bad connection, possibly a terminal pushout in the connector or broken wire. If you want to check some things out before taking it in for warranty repair, I'd locate the module and check the harness to module connection. Gently pull on each wire to see if any are not locked in to the connector (terminal pushout), and visually inspect for any damage to the wires.
Jerry