Measure operations won't work
Problem: I couldn't select, add or delete measures.
Workaround: Try going from "page view" to "continuous view" and trying your select, add or delete there. This worked for me and afterward I went from "continuous view" back to "page view" with no problem. It does require flipping back and forth between page view and continuous view and back to page view (if that's what you're working in), but if you don't add or delete measures that often, it's not a big problem.
The "page view"/"continuous view" button (on my computer) is just below the "Help" menu item at the top of my screen (I don't know the name of which toolbar it's on). When you click on it, you'll see a dropdown menu showing the "page view" and "continuous view" menu options.
I was using Musescore 2.0.3, Revision 3c7a69d on a Windows 10 operating system. Don't know why the problem happened, but I couldn't find anything in the handbook, forums or on an internet search that addressed this problem, so thought I might save someone else some frustration.
Comments
I've never seen that happen before. I've always been able to add and delete measures in every view.
In reply to I've never seen that happen by mike320
By chance, would not you be in a score where you would have ticked "Hide empty staves" in: Style / General / Score ?
In this case, by appending measures, they are added, but you do not see it. By switching to "Continuous View", you see them now.
So, first check this: untick this option of hide empty staves, and this behavior will no longer manifest (if it is the one you describe)
Then, when you say you cannot select a measure/measures, it may be different. These can be corrupt measures, or possibly other issues. In this case, it would be useful to show/attach a particular score demonstrating this.
Any way: an advice: updating to the 2.1 version