Bar won't let me put anything in it

Hi everyone,

I've been using MuseScore for almost 2 years now and while I've been pretty happy with it I do run across the occasional bug. At the moment I'm working on a bigband arrangement and there's two bars for guitar, piano and bass that won't let me input anything. I've tried deleting the bars and the instruments and put them back again but to no avail.

If anyone has a good suggestion I'd be very grateful!

Maarten