I did some digging around for this one and found a few crafty articles about adjusting throttling policies using PowerShell and making changes through ADSIEdit (http://reidablog.blogspot.com/). However, none of these seemed to fix my issue.
We had a newly built Exchange 2010 SP1 server which was ready to go into production but kept throwing the error when attempting to use PowerShell. Two other servers appeared to be running fine.
The server had recently received a new SSL certificate using the Exchange 2010 certificate provisioning and assignment process in the GUI. Unfortunately the IIS service hadn't been restarted yet and the URL used for remote PowerShell was using a certificate which wasn't trusted or valid anymore.
A quick "IISRESET" on the server resulted in my fix.