I just the attached screenshot error message while editing on Windows, right after I pressed "Ctrl-S" to save my file.
You can see from the screenshot that the build tab is shown, so I don't know why it says it must be active.
After hitting "OK", I tried "Ctrl+S" a 2nd time, and there didn't see to be an issue.
I don't have the latest hot fix installed, I will try that
