Hi,
How are you setting the CONFIG bits of the chip? Within your code, or thru PICStart interface in MPLAB or not at all (ie. you're relying on the defaults)?

What's the frequency of your oscillator?
PBP3 defaults to XT_OSC for the 877A, if you're running with a high frequency crystal, like 20MHz then you need HS_OSC instead.

/Henrik.