Error:The Citrix servers reported that they are too busy to provide access to the selected resource

I came across this error in a Mixed 4.0 / 4.5 MPS Farm. The users would try to access the 4.5 server (which was the only 4.5 server in the farm) and they would receive this error message.
The complete error was:
The Citrix servers reported that they are too busy to provide access to the selected resource. This message was reported from the XML Service at address http://someotherserver:80 [com.citrix.xml.NFuseProtocol.RequestAddress]. 

So what can we do about this error?

I tried a number of things that didn’t help:
– Wishing it wasn’t a mixed environment in the first place..oddly this did not help
– Pointing the XML server of that specific WebInterface to the Server it was unable to connect to…nada….
– IISReset…no dice….
– Restarting IMA on the server..nope wrong answer….
– I knew there were some custom load balancing policies active on the Farm so I tried adjusting 1 item on the assigned policy to see if that would help…naaah not to much….
dn
Last thing I tried was assigning one of the default Load Balancer Policies to the affected Server and behold..users were able to happily login again..!
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