When my character open the Redoran Refugee door, the games crashes. How to resolve it?

Turn off the Autosaves.

Also, go to another cell and wait 73 hours if it still crashes to clear out any scripts.

this is a joke?

Yeah, moderators are always doing that. Silly moderators.

and... how to fix this?

Did you read my post and try what I suggested?

Dude, he's not trolling. Probably...
He's a Mod after all.

Just take his word for it will ya

yes, but... 72 real hours or game hours?

In game hours.
Remember in Oblivion how a cell would reset after 73 game hours?
If you did not enter a cleared dungeon in 73 game hours, the denizens would respawn.

Skyrim has a similar feature, though the respawn time is longer.
You can try 73 hours, but as the reset time is about an in-game month I would suggest finding an indoor location and waiting there for an in-game month, this to 'reset' the rest of the world.

Disabling autosaves really helps with savegame bloating and loading times.
For best performance, disable all autosaves.
Get used to saving manually, and regularly.
Also, do not overwrite saves, but delete old ones as you make new ones.

im probing this method, but the games crashes =

Its not a 100% guaranteed fix, just something that may help the game run smoother.

You can also try reloading a save from before you got the quest.
Good luck