Almagest's page

My group is looking for 1-2 GMs, players, and players who'd like to join a rotating GM schedule for our weekly/bi-weekly game. We use Maptool to handle our combat, though someone with a nice battlemat+dry erase, or printed maps, or 3-D paper maps, or foamcore/purchased plaster or stone scenery/whatever is welcome as well. As long as we have something that looks nice and helps organize combat, we're happy.
Our games generally focus more on combat and dungeon-crawling, but someone who can run a game with a kickass storyline & an increased emphasis on roleplay is very welcome -- same goes for any players who'd like to add roleplay to our games. Lead by example!
We play Friday nights, mostly weekly, from 7 PM until whenever. We could possibly switch to Saturday or Sunday, though all players would have to agree. Location is ~2 miles north of Wrigley Field.

My campaign was brought to a standstill tonight because of the following scenario:

-Enemy is holding an improvised grenade weapon
-Enemy uses move action to open a door in front of him, then standard action to toss the item at a PC in front of him.

I ruled that no attack of opportunity was allowed for the PC, even though ranged weapons within threat range normally allow AoO, since:

-The opponent had total cover from the PC before the door was opened
-The PC didn't know the opponent was there
-Opening a door does not provoke an AoO
-Any kind of cover does not allow for an AoO
-

Remember that even actions that normally provoke attacks of opportunity may have exceptions to this rule.

The player (who wasn't even the PC in question] argued that there should be an AoO, since the PC now knew the enemy was there after the door was opened.

This small issue ended up stopping the game for a good 15 minutes, as the player in question wouldn't let the issue go, even though everyone else at the table (even the player controlling the PC in question) agreed with me. What's your opinion? Did I make the right call? Is there a rule or concept I'm missing? Thanks.