I was trying to add some externals sources to a Sharepoint list and ran into the error “Business Data Connectivity Metadata Store is currently unavailable”.
I was getting this error in both SPD and the Web Interface. After looking through the Admin Panel, I noticed that the “Business Data Connectivity Service” was running under “Central Administration -> Services”, but, there was no “Business Data Connectivity Service Application” under “Central Administration -> Service Applications” (this is because I’m pretty sure I did not add the BDCS when i created the site, but it’s normally there by default)
Lastly, make sure that the newly created BDCS is associated (checked) with your Web Application by going to “Central Administration -> Manage Web Applications” and clicking on Service Connections
So after creating a new “BDCS”, the error went away.
Another way to fix this, just run the configuration wizard and it should create one for you.