This solution applies to installing the Barracuda Spam and Virus Firewall Anti-Virus Agent onto an Exchange 2013 server.
When installing the plug-in on certain Exchange mail servers 2010/2013 there can be an error from the transport agent. It will appear to successfully connect and download the virusdefs but fail before completing with the following error:
?Connecting to remote server failed with the following error message: the WS-management service cannot process the request. The load quota for the system has been exceeded. Send future requests at a slower rate or raise the system quota.?
Go to the Application Pools find the MSExchangePowerShellAppPool. use right click to recycle this AppPool. You should be able to complete the install after this point.
Attached is an image as an example of said error
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