This comes up every now and again on the TechNet forums, different quirks and oddities related to Lync 2013 conference IDs. Perhaps A new meeting configuration has been put in place, but the changes don’t seem to take effect for a user. Perhaps a user creates a conference, but gets the old “We’re having trouble getting you into the meeting. It’s possible you’re using a bad URL. “. I’ve even seen a case where two users somehow got the same external conference ID. I’m still not sure how that one happened, perhaps admin tampering?
There’s a quick fix before you spend hours troubleshooting, just reset the conference ID. This seems to fix 99% of these issues. Have the users navigate to the dialin.domain.com page, sign in and click the “Reset my Assigned Conference information” link. That’s it.
Figure 1: What frustration looks like (I AM THE ADMIN).