can someone please explain this error to me

[kwallace1984]

[COLOR=#000000]System.NullReferenceExeption: Object reference no set to an instance of an object. at COServerProject.Client.GetPacket(Byte[] data) in c:\xxx\client.cs:line 7785[/COLOR]

I need specifics. All my reading has told me is that this error occurs when a string is not null. Knowing the quick fix would be nice, but understanding the error would pwn.

Thanks in advance for your helpful replies.