Hi Abhij,
While it is possible to have more than 1 "weak" Verbal category, at that scoring level, it's not likely (and by "weak", I mean getting fewer than half of the questions correct).
Test Takers who score in the V20-V29 range (or lower) are losing points in all 3 categories, so in that situation, 2 (or 3) weak categories is more common.
In the Verbal section, missed points can be due to a variety of factors: grammar knowledge (for SCs), lack of note-taking (RC,CR), not really understanding what the question is asking for (RC, CR), fatigue, pacing problems, not knowing how to spot the wrong answers, etc.
All of these problems can be fixed, but that process is usually about learning the proper tactics for dealing with the various question types AND dealing with the section as a whole. As such, self-studiers normally can't fix these problems on their own.
GMAT assassins aren't born, they're made,
Rich