Problem with Formula that displays contents from some cells but not others

[nje]

I'm having a lot of problems with this project.
A lot (most ) of my formulas have be obtained with the kind help of the forum users on here and then I have adapted some, not too succesfully to meet the needs of other things I've dreamt up.
In the Tech Log sheet of the attached sample I can't work out why the formula won't work in columns starting at B6, D6, and E6 when it works in works in F and I
I have other problems in the Pilot sheets but that is for another post, I can't see what is wrong, could someone point it out to me please
Thanks