I am sure you have checked these things, but just to throw them out there. Is there another object somewhere in your solution with the same name causing a reference issue like a business object with the same name? Is the Advisors.cs accessible (public)?

Yes - already checked this

Out of curiosity, what is in your MainForm.cs that is referencing this object?

It is a menuitem click event handler - MainForm is an MDI Container - it just calls other forms from its menu...