If this is with the .NET client 2.4.7, you might try a downgrade to 2.4.6 if it’s easy to do so. I don’t think it’d be related, but there is a known issue with single-node-clusters in 2.4.7. The release notes have details.
If there isn’t any difference, then can you give us an indication of what it’s failing with? Perhaps increase the log level too in order to get more info.