Hi Nishant,
Since this most recent score is considerably lower than your other scores, it's important to really define HOW you took each of these CATs, so that you can look for a pattern or possible explanation for what happened.
The first thing to notice is that this was a GMAC CAT while the other two were Veritas CATs. That point doesn't prove anything, in and of itself, so you have to go deeper into the details.
For example:
1) Did you take each CAT in its ENTIRETY (meaning you took the Essay and IR sections too)?
2) What were the Scaled Scores on each of the CATs?
3) What time of day did you start each CAT?
4) Was the location different?
5) Were there any distractions?
6) Was there any aspect of taking the CAT that would be considered unrealistic (pausing the CAT, listening to music, drinking coffee while taking it, etc.)?
7) After reviewing the CAT, how many questions did you get wrong because of a silly/little mistake? How many times did this happen on the other CATs?
It's possible that you just had a "bad day", but it's also possible that you're studying (and taking your CATs) in an inconsistent or incorrect manner. Whatever caused this score drop needs to be weeded out and removed.
GMAT assassins aren't born, they're made,
Rich