After Install OV_client_SDK(3.0.1.42000)


DOS mode - cd into the 
cd Program Files\ObjectVideo\Client SDK\bin
or
cd Program Files\ObjectVideo\Alert SDK\bin


and type register the LIB as following
c:\Windows\Microsoft.NET\Framework\v1.1.4322\regasm .\ClientSDKXML.dll/tlb:ClientSDKXML.tlb