Modify statement going into dump

Weired thinigs happen to you and you are left clueless on the root cause. This happens to me when I was doing routine coding and all ofa sudden Modify statement starts giving dump.

Lots of head scratching finally got to know the reason.

Below is my coding.

The reason is that I was doing loop on one internal table and was trying to upadte the other internal table inside that loop.

The Purpose of MODIFY statement is to modify the internal table content with in the particular loop of the internal table.

The reason for dump is I was trying to modify the unknown internal table directly.

So when I change the coding like in below screen shot, it works.