Errors in c#

Question

Hi friends ,
When i open my project , any form contained my class is noticed with errors , some of that are like this :

Could not find type 'ERP2010_11.Class.Class_GPPanel'. Please make sure that the assembly that contains this type is referenced. If this type is a part of your development project, make sure that the project has been successfully built.

		The variable 'GP_Noidung' is either undeclared or was never assigned.

I do not know how to solve this , I can not open any form at this time . I need help from you all , Thanks .