I have two thoughts initially...

1. That initial Pause 100 is far too short.... increase it to Pause 2000 at first, you can then pare it back to Pause 1000 if it does the trick.

2. Don't tamper with the LCD Port pins manually, leave it to PICBasic. You've got the data pins on PortD, you then manually set the WHOLE of PortD to zero with...

PORTD = 0 ' All LEDs off

Don't do it. Set the non-LCD pins individually and don't play with the LCD pins unless you know what you're doing... ie...

PortD.0=0
PortD.1=0 etc etc.

Better still... define those pins at the start of your program... eg...

LEDA var PortD.0
LEDB var PortD.1 etc etc

then within your program you can just refer to the aliases...

Low LEDA
Low LEDB and so forth.