Error: 'The plug-in argument HotfixrootFolderPath has invalid value .' won't go away.

I could someone's expert opinion on this issue.

I've followed the instructions from the excellent article but something isn't lining up right. Each time I try to preview updates using CAU, it fails with this error. I don't get why this is happening. 

Here are the reported values for my Cluster Aware Updating settings. I do in fact have a path configured, as you can see.

Name  : CauPluginName
Value : {Microsoft.HotfixPlugin, Microsoft.WindowsUpdatePlugin}

Name  : CauPluginArguments
Value : @{ 'HotfixConfigFileName' = 'DefaultHotfixConfig.xml'; 'DisableAclChecks' = 'False';'HotfixRootFolderPath' =
        '\\mgmtdc01\cau-hotfixes'; 'RequireSmbEncryption' = 'False' }

I can browse that folder path, but CAU doesn't think its there. I originally wanted this to be a hidden share but even after removing the share character '$' it didn't improve the situation.

Why is CAU Preview unable to see the setting I've configured?

Please help me see what I'm missing! Thank you in advance!