Topic Title

I think that this message means someone has clicked the "Watch this forum for posts" link in the lower left of the DDN Discussion forum page, but they do not have a valid email address in their user profile. As a result, when the forum software tries to send the user an email notification that there is a new post in the forum, it encounters an error.

I tested the function and got the same error, but it did not prevent my message from being posted. Unfortunately, I don't have tools that tell me which users have signed up to receive notification of posts in the DDN forum, so I don't know which account is causing the error.

Is everyone that signed up to receive email notifications actually receiving them? If anyone isn't, check your user account profile and verify that it contains a valid email address.

I think you have misunderstood my reply.

You are not causing the error, you are receiving it. Some other forum member has entered an invalid email address in their user profile, and that is the cause of the error. When you try to post a message, the forum attempts to notify that other user. It fails because of the invalid email address, and you receive the error because you are the one entering the post.