With so little information, there's no way to know.

Have you verified the items on the ICSP page?

In-Circuit Serial Programming (ICSP)
http://melabs.com/support/icsp.htm

Have you set your configs?

Specifying configuration bit settings in PICBASIC PRO™ programs.
http://www.melabs.com/support/config_defaults.htm

Have you disabled the Analog inputs?

All Digital
http://www.picbasic.co.uk/forum/showthread.php?t=11100
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