Strange and probably dumb question

What is this black line, and how do I get rid of it?

It marks a time signature change. If you didn't mean to force 4/4 there (like if the time signature was already 4/4), edit the time signature marker and uncheck "set time signature".

I use it to signify when it's time to take a Tea break! :) Bar 18 is a bit early though.

But wow, what a strange and probably dumb question. ;) [hey, you didn't have to short sell yourself. It's a good question]