There Was an Error Delivering Your Message (7000)

This error message can appear if the recipient has you blocked, if your account has parental controls, or if chat is disabled in your privacy settings.

Message your friend outside of Battle.net to have them check if you are blocked. If they do have you blocked, they can unblock you by following the instructions here.

If your account has parental controls, the communication settings would have to be adjusted through the Parental Portal.

Lastly, you can check your communication settings through your account management site here.

If the error message persists after checking the above, please report the issue by posting on the Desktop App Bug Report forum.