You have two IF's but only one ENDIF, so that would error...

Try this... which includes a few additional things to think about....

Code:
	ButtonA var PORTB.0
	LED1 var PORTB.1
	LED2 var PORTB.2

	TRISB=%00000001

Loop:
	If ButtonA=1 then
		High LED1
		LOW LED2
		else
		LOW LED1
		HIGH LED2
		endif
	Goto Loop

	End
Finally, check your PBP manual - BUTTON is a reserved word, you can't use it as a variable.