You need to restart your Connector. 

This can be accomplished by:
  1. Stop/Restart the Host on the server
    • In Scheduler, choose File>Stop Host.  Then, choose File>Start Host
  2. If the stop/start does not work, then complete the following on the server
    1. Go to Start>Run
    2. Type services.msc
    3. On this list, double click "Integration Service [your account id]"
    4. Click Stop

Now, go back to Scheduler, and you should be able to initiate a sync or send your mapping metadata. If not, Click Create a Case in the Additional Assistance box on the right. Reference this solution ID, and a support analyst will contact you.

If that doesn't resolve the issue, chat with Support and reference this article.