Unable to create Release object using OTAClient.dll in c#

Hi,

this is the code i am using after connected to the project in order to create a new release object but for some reason i am getting this exception 

ReleaseFactory relFactory = con.ReleaseFactory as ReleaseFactory;

Release rel = relFactory.AddItem(DBNull.Value) as Release;

the exception : Exception from HRESULT: 0x80040057

any ideas ? :) 

Thanks in advance,

Ofir