G'day,
My honeywell TCAS II manual states the following:
"RA FAIL will appear when the TCAS cannot post Resolution Advisories"
Further on it mentions that loss of vertical speed information will result in a RA fail indication although the wording suggests that this isn't the only case you'd get a RA FAIL indication. Doesn't really help much with the answers given in your question though!
"INCREASE DESCENT - INCREASE DESCENT" = Increase descent to that shown by the green arc on the RA indicators, from 2500 to 3000 FPM
Cheers
C & B