New Post: Client failed to connect

In the tools > settings window, in the Authentication Settings tab, which option radio button is selected? In there, there's the option to use the current credentials, specify a username and password, or ask each time.

WPP uses WMI to create the remote process. See if you can execute the following command using the same user and same machine (replace [computername] with the name of a remote system that's failing):

wmic /implevel:impersonate /privileges:enable /node:[computername] process call create "WuAuClt /DetectNow"

If you have an error there, you should troubleshoot that, since that's essentially what WPP does to force a remote detection, at least from what I can glean from the currently posted source code. If that command works, and WPP still gives you that error, then... something fishy is happening!