Nhibernate错误：找不到给定标识符的行错误

I know that this question is repeated one. But no one could answer briefly enough to answer corrctly. I am getting Nhibernate error " No row with given identiifer found error" when im trying to use the guid to give me the record from the table. I am using Nhibernate load function to load the record with the unique identifier(GUID) but if the record is not there it is giving exception. Am I missing some property in hbm.xml file?I know that this question is repeated one. But