how do I adjust measure width

I create 3 or 4 part vocal scores. I often adjust the width of a measure, or number of bars in a line, with no problem, using shift + {
Sometimes, for no reason I can see, it simply refuses to adjust for me.
is there a work around?
In the attached score, I want to set it for 4 bars per line and I can't shrink m. 13.