Swift Framework: Umbrella header '[...].h' not found

This usually happens after a project rename or something like that. The problem is that the umbrella header is no longer listed as a Public header. Check the attached image to see how to fix this.

In Xcode 7 Beta, with Swift 2, it will also happen if your Framework Header is not declared as "Public"

For instance, I had a Cocoa Touch Framework with a "Project" visibility for the header file, and the error "Umbrella Header ... not found" for all Swift files in my project, once I had the header "Public", the error went away