Hi,

Could not find the code you are using in my manual?
But, the chip you are using 16F648 does not show up at MICROCHIP, the A version does. If it is the "A" version there are a couple of comparators on PORTA.

You will need to turn the comparators off to make PORTA.0 and PORTA.1 regular I/Os.
Code:
CMCON = 7
Should be at the top of your code.

If this is the problem here are two post that will explain more.
http://www.picbasic.co.uk/forum/showthread.php?t=561
http://www.picbasic.co.uk/forum/showthread.php?t=562

POTRA has some different things than the other PORTS.