Do you have the pins connected to anything? It smells like the good old Read-Modify-Write problem...

What if you try:
Code:
trisa=0
main:
   porta.0=0
   Pause 1    'Allow PortA.0 to settle low.
   porta.1=0
   pause 10
   porta.0=1  'Allow PortA.0 to settle high
   Pause 1
   porta.1=1
   pause 10
   goto main
HIGH and LOW also resets the corresponding bit in the TRIS register (making the pin output) for you so even if you have the pin setup as an input doing HIGH PortX.x will switch it to an ouptut and set it high. I'm not sure WHY it matters in THIS case but we can figure that out IF it turns out to BE a RMW-problem.

/Henrik.