WCF web service fail run from the IIS because could not load DLL?

I wrote some WCF application. I registered the application on the IIS.

The WCF application is build by using some dll that i wrote in the past. I created reference to th开发者_运维知识库em and its seems that all work fine when i start the application thru the visual studio 2010.

But when i run it thru the IIS - i get message about some DLL that missing - even if the DLL it clearly in the project.

What i can do to fix it ? I remove the reference - and load it again - and still nothing help.

Thanks for any help.

Is the DLL/Reference marked as Copy Always in properties? This will force the DLL to copy to the bin folder which IIS will require for a non-GAC'd assembly