Terraria.exe #22

When i modify terraria it gives me an exception "Terraria.exe has thrown an exception" ? it used to work, it works without editing it, i used my own source,

System.TypeInitializationException was unhandled
Message=The type initializer for 'Terraria.Main' threw an exception.
Source=WindowsGame3
TypeName=Terraria.Main
StackTrace:
at Terraria.Main..ctor()
at Terraria.Program.Main(String[] args) in C:\Users\Mel\Desktop\C# stuffs\Terraria Clean Source\WindowsGame3\WindowsGame3\WindowsGame3\Program.cs:line 9
InnerException: System.NullReferenceException
Message=Object reference not set to an instance of an object.
Source=WindowsGame3
StackTrace:
at Terraria.Item.SetDefaults(String ItemName) in C:\Users\Mel\Desktop\C# stuffs\Terraria Clean Source\WindowsGame3\WindowsGame3\WindowsGame3\Item.cs:line 456
at Terraria.Player..ctor() in C:\Users\Mel\Desktop\C# stuffs\Terraria Clean Source\WindowsGame3\WindowsGame3\WindowsGame3\Player.cs:line 219
at Terraria.Main..cctor() in C:\Users\Mel\Desktop\C# stuffs\Terraria Clean Source\WindowsGame3\WindowsGame3\WindowsGame3\Main.cs:line 70
InnerException:

sorry .. im a noob xD