This folder should contain the following files for each Exchange version:
Microsoft.Exchange.Data.Common.dll
Microsoft.Exchange.Data.Common.xml
Microsoft.Exchange.Data.Transport.dll
Microsoft.Exchange.Data.Transport.xml

The expected folder structure is:
Exchange 2007 with SP3
Lib\Exchange 2007 SP3\Microsoft.Exchange.Data.*

Exchange 2010 without any SP
Lib\Exchange 2010\Microsoft.Exchange.Data.*

Exchange 2010 with SP3
Lib\Exchange 2010 SP3\Microsoft.Exchange.Data.*