Hi Anit,
Can you please explain what you want to do when you face this error?
It seems that you are using HEE Standalone version, in this case you have to create server groups for exchange hosting under Service Director menu. Once a server group added you can create plans for Exchangs Hosting. If you are facing this problem when creating service plan for exchange hosting do follow above procedure and you will be ready to go.
If this does not solve your problem then please explain where you face your error using screen shots.
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M. Usman
Senior Software Engineer
MachSol, Inc.