I started using NHibernate and I keep on getting the following error: MappingException: Unkown Entity Class [ClassName]

I started using NHibernate and I keep on getting the following error:

MappingException: Unkown Entity Class [ClassName]

I check my mapping hbm.xml files several times but could not figure out the problem. Finally, I found out that the problem was not in the hbm file but it was because I was not setting the hbm file as an embedded resource. I simply right clicked on the hbm file and selected properties and set the "Build Action" to "Embedded Resource". That's it problem solved!