Hi,
I have been looking of a solution of this problem, that started from a new installation of Exchange 2013 (CU8 installed).
I get this errors after 30 seconds in (run as admin) management shell.
Starting a command on the remote server failed with the following error message :
[ClientAccessServer=SERVER,BackEndServer=server.xxxx.com,RequestId=9d3d4900-3e71-4344-b607-72c54351ec3e,TimeStamp=8/16/2015 1:57:55 PM] [FailureCategory=WSMan-InvalidShellID] The request for
the Windows Remote Shell with ShellId B39DBE1D-CED0-4F26-A8AE-8AB7F939E8F4 failed because the shell was not found on the server. Possible causes are: the specified ShellId is incorrect or the shell
no longer exists on the server. Provide the correct ShellId or create a new shell and retry the operation. For more information, see the about_Remote_Troubleshooting Help topic.
+ CategoryInfo : OperationStopped: (server.xxxx.com:String) [], PSRemotingTransportException
+ FullyQualifiedErrorId : JobFailure
+ PSComputerName : server.xxxx.com
Sofar I found this problem listed in an MS article about language cookies, solved with CU3.