The "Unable to find the requested .Net  Framework Data Provider. It may not be installed" (Screenshot attached. Filename: Error_screenshot.png) error is thrown when attempting to open a file from the library or trying to save a file to the library with the installed Analyst/Professional client.

This is caused because the machine.config file, which is a configuration file of the .NET framework, becomes corrupted with unnecessary additions in the machine.config file.

1) Open the machine.config file located at C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config
2) Look for the following lines of code.

<system.data>
        <DbProviderFactories>
            <xxxxx>

        </DbProviderFactories>

      </DbProviderFactories>

       </DbProviderFactories>

 3) Make sure there is single entry of:

</DbProviderFactories> and delete additional </DbProviderFactories>

In other cases, the following value is seen.   

</DbProviderFactories>


     </DbProviderFactories/>.... (Delete this entry.)

NOTE:

 - We recommend making a backup of the machine.config file.
 - Edit the machine.config file in any XML or plain-text editor tool.
 

Unable to find the requested .Net Framework Data Provider. It may not be installed.

External: 'DbProviderFactories' section can only appear once per config file error:

•  http://forums.asp.net/t/1693277.aspx/1