Hi,
have U checked with multimeter that U are getting proper voltage on
wiper of POT? Unless that is confirmed then no use of banging head like
Mister_E on program and PIC. ;-)
It is possible that pot has mechanical problems at ground end and
after wiper moves few turns the ground end opens and U get full voltage
on wiper!!
As U are getting upto say number 10 then this is a probability.