Let me piggyback on Wayne's question:

My song is in 4/4 but I am unable to insert a single bar of 6/4.

Page 166 of hard copy Windows 2016 says all I have to do is open the "Set Time.." window at the desired bar, hit 6/4 and I'm done - NOT.

At the target bar and the next 2, I get a red underline and no 6/4. I tried inserting a a bar of 2/4 but that doesn't work either. It's as if the program is not accepting my command.

I also tried the solution given below to Wayne without success. Hope someone can help. Thx.