What I am trying to say is that the 887 and 877A are not exactly identical. The MCLR input (something that can be associated with such problems) are quite different on both devices. My suggestion is to connect the MCLR to Vdd on the 877A using the R-C-R circuitry in the datacheet.

Also, the OSC input circuitry are not the same on both devices. Do both circuits you have (i.e. working 887 and non-working 877A) use the same external crystal circuit, or does the 887 uses the internal oscillator?

The code you have posted works on the 887, but not on the 877A? Is this correct?