WMI StdRegProv not found!

If you're trying to do registry stuff on a remote system, you may not have sufficient privileges. I would break your code down into parts, all contained in a try/catch block.

Is there an inner exception?

BTW, I found this with google:

public static string ConnectToRegistry (string servername)
{
    string regKeyToGet, keyToRead;
    ConnectionOptions oConn = new ConnectionOptions();
    oConn.Username = "admin";
    oConn.Password = "pass";
    ManagementScope scope = new ManagementScope(@"//" + servername + 
                                                @"/root/default", 
                                                oConn);
    registry = new ManagementClass(scope, 
                                   new ManagementPath("StdRegProv"), 
                                   null);

    // Returns a specific value for a specified key
    ManagementBaseObject inParams = registry.GetMethodParameters("GetStringValue");
    inParams["sSubKeyName"] = regKeyToGet;
    inParams["sValueName"] = keyToRead;
    ManagementBaseObject outParams = registry.InvokeMethod("GetStringValue", inParams, null);

    return outParams["sValue"].ToString();
}