From the last line of your included code - the beginning (often) of the error that propagates through all those other references:
at Assistant_Accountant_V1._0.Program.Main() in E:\C# Project\Assistant_Accountant_V1.0\Assistant_Accountant_V1.0\Program.cs:line 18
This reference may well show you what has the problem at runtime. Did you give this a look?