[Squirrel]

Set these OnPlayerConnect

PHP код:

SetVirtualWorld(playerid, 0); 


Also use

PHP код:

OnPlayerObjectsLoaded 


It's not part of SA:MP and you must look for it.
It will help you with falling thru the ground. Problem is that there is certain object that you are spawning on or wrong coordinates of your spawn. Check those FS's if there is any coordinates that could mess up player on Spawn with some random coordinates.