Alberto, it would be hard to use sed( s/^I$// ), because there is no explicit NULL value and there are many NULLs in the last column.
So i can't be sure how many tabs should be in the end of each line.
Yes, Karsten, maybe scripting would be the easiest way to fix this, i would then probably insert this line for line. That's a possibility. It might take a long time to run, but that's not much of an issue.
