I have faced my previous assignment so that I followed the below instruction , so that problem has been resolved.
Outlook client applications cannot connect to public folders
The issue occurs because the Microsoft Exchange RPC Client Access service acts as a proxy for earlier versions of the Availability service (free/busy information). Therefore, if you have a public folder that is installed on an Exchange Server 2010 server, the Microsoft Exchange RPC Client Access service intercepts the free/busy information requests.
You require disabling the Availability service calls as follows:
1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeRPC\
3. On the Edit menu, point to New, and then click Key.
4. Type ParametersSystem, and then press Enter.
5. Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeRPC\ParametersSystem
6. On the Edit menu, point to New, and then click Dword Value.
7. Type DisableAvailabilityServiceCalls, and then press Enter.
8. In the details pane, right-click DisableAvailabilityServiceCalls, and then click Modify.
9. In the Value data box, type 1, and then click OK.
10. Exit Registry Editor.
I would like thanks to Microsoft Support team