I am running v15.4 and having the same issue.
When trying to add a contact from the email within SmarterMail interface, I get error.
Oops!
There was an issue that caused this page to malfunction.
Administrators
This error has been logged and can be found in the View Logs page as well as in the file system. If you have questions, please refer to the
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ERROR LOG FILE
I cannot add because cannot have links in my reply