Event ID - 8275

Event Id8275
SourceMSExchangeFBPublish
DescriptionSchedulePlusFreeBusy folder could not be opened for duplicate message deletion on virtual machine <server name>. The error number is <error code>.
For more information, click http://www.microsoft.com/contentredirect.asp.
Event InformationError: 0x80004005 = "Unspecified error"-  This error shows that a system public folder has been deleted and it may not be able to recreated.

Error: 0x80040115, indicates a problem with network connectivity.

See links given below for more information out of that "Resetting System Folder structure" can applied as a last resort.
Reference Links Exmerge Loses Free/Busy Information for Existing Appointments

How do I delete a bad Schedule + message? from WindowsITPro

How to Reset System Folders on an Exchange 2000 Server

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