I'c check these posts to see if anything inside helps, some thoughts are resetting the conference ID on the dialin.sipdomain.com page, and rerunning Step 2 of the deployment wizard.
https://social.technet.microsoft.com/Forums/lync/en-US/64572372-c756-4289-b447-0d743a53925d/lync-web-scheduler-unable-to-create-meeting?forum=lyncdeploy
https://social.technet.microsoft.com/Forums/lync/en-US/67d67764-e19a-4f3e-9d1b-ef320f1e8f2c/web-scheduler-the-meeting-information-could-not-be-saved-please-try-again?forum=ocsconferencing
https://qa.social.technet.microsoft.com/Forums/office/en-US/e6d1c21e-3c04-42a6-8d5e-868f58c997dd/web-scheduler-has-been-released-for-lync-2010?forum=ocsconferencing
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SWC Unified Communications This forum post is based upon my personal experience and does not necessarily reflect the opinion or view of Microsoft, SWC, their employees, or other MVPs.
