Issue
Underlying Provider Failed On Open
Solution
It has been observed, in some environments, the removal of the "Network Library" SQL Connection String parameter can resolve issues with SQL connectivity for the Service and UI on a clean install.
In certain cases, this setting renders the SQL connection in a failed state and results in the inability to configure the product.
This can be observed as SQL Exceptions in the Application Event Logs and a message "Underlying Provider Failed On Open" when attempting to install a license file.
Create a backup and modify the E2EConnectionStrings.config file in the product installation directory 'bin' folder.
There will be two references to 'Network Library=dbmssocn;'
Find these references and remove including the trailing ; delimiter.
Restart the Exchange Pro MCP service and perform an 'iisreset' at an administrative command prompt.
If this does not solve your issue, revert the file to the backup and restart the service/perform iisreset.
There are many reason for the error 'Underlying Provider Failed On Open', this is one possible solution.
