Q: iMessage not working on iPad Mini or Macbook Pro, works fine on iPhone 5S

Since the beginning of April, I haven't been able to send or receive iMessages on my Macbook Pro or my iPad. They do not receive any incoming messages or have the ability to send out any messages. Every time I try to send a message to a phone number REGISTERED WITH IMESSAGE, this error message pops up.

Even though iMessage refuses to work on both my iPad and my Macbook, it has been working flawlessly on my iPhone. Every number that I try (and fail) to send an iMessage to on both my iPad and my Macbook, I have been successfully able to send a message to on my iPhone with no problem.

This is what gets me: I have signed in to my Mac and my iPad with several other Apple IDs and iMessage works FINE when there is another Apple ID involved. There is no problem when someone else signs in using their Apple ID.

So far, the only thing that has been affected is iMessage. All other aspects of iCloud work great. FaceTime hasn't stopped working once, for example.

I have literally tried everything. I have been on every single discussion about this topic. I have had two separate cases with Apple Support about this issue. I have brought all my machines to the apple store TWICE, and they still couldn't figure out what was wrong.

I guess I'm just hoping that somebody out there will know what's going on here. Please help!!