Unexpected error during publish. Sequence contains more than one matching element.

This error is produced when a server name has been typed in the Assemble add-in server field more than once.

To resolve this issue:

1.  Navigate to C:\%localappdata%\Assemble\ from Windows Explorer.

2.  Delete the Connections.xml file.

3.  Publish your model, but you will need to re-enter your server name.

4.  In future publishes, be sure to use the server name from your drop-down list in lieu of re-typing the server name.