GPG Mail can't decrypt message
Sometimes things go wrong and a message is not decrypted along with an error message
Secret key to decrypt the message is missing.
Various circumstances can cause this error with the most likely being, that the message author used the wrong public key to encrypt the message in question. Since the corresponding secret key does not exist on your system, you are unable to decrypt that message.
When multiple public keys for your email address exist, your contact may be using an old key of yours, which you have replaced a while ago.
Or your secret key got lost on your local machine. This can happen after moving to a new computer but forgetting to transfer your secret keys. In that case you would need to recover your secret keys from a backup.
We recommend to upload and verify your current key on the key server.
To ensure your contact is using the correct public key of yours, we suggest to verify and sign each others public keys.