App Store: The product distribution file could not be verified. It may be damaged or was not signed.

Greetings,

I am trying to Re-Install FCPX. I get the following message: "The product distribution file could not be verified. It may be damaged or was not signed."

I originally tried to update it, but I got the same message. So I removed it from applications but I still get the same message when trying to install from App Store. I have bought FCPX so definitely registered under our username.

I tried all solutions in Apple Communities and elsewhere including:

- Clearing App Store Cache (Didn't Work)

- Looking at console and finding the folder with an error (Didn't Work)

- I updated to El Capitan from Yosemite in the hope that the newer OS might offer some solution (Didn't Work)

- I repaired permissions (Didn't Work)

- I went into Safe Mode and tried to install from there (Didn't Work)

Can someone please help me 😟

Best,

Saleh.