MPASM is very syntax sensitive when it comes to the INC file.
A few things:
make sure _XT_OSC     EQU     H'3FFD' is in the p16f84.inc file, or that
you are using the original INC file.
MPLAB must be able to find the INC file (I always open mine, as I put
all my register declarations in it).
I notice you got _CONFIG instead of __CONFIG (one dash instead of two,
this could be your problem).
Use the c:/MPLAB/template/f84temp.asm for your programs, or copy the
__CONFIG... line from it, and then make your changes, and follow the
syntax in the INC file under "Configuration Bits".

Basically, I always use both the INC and template files, make
modifications to my liking and save it for future use before I put any
code in it. I then run both side by side when I do my editing. A very
nice feature to use.

Hope this helps
Quentin