Build operations are disabled:'project.xcworkspace' has changed and is reloading

I have the exact same issue with Xcode 7.3.

Restarting the IDE helps.

I had similar issue with Xcode 9.3 and solution mentioned by @sssliver didn’t worked.

Below is solution that worked :

1. Quit Xcode (cmd + Q) and reopen project
2. Delete derived data content.
3. Clean project (cmd + shift + K)
4. Build project (cmd + B)

On Xcode 11 when I changed my app folder location, I got this error and thats was because Swift Package Manager was redownloading my project libraries, once it finished downloading, it worked again...