you don't even know what addons you are using?
Ok, do the following then:
A) Run blockland normally, start your server, and get your friend to connect, which should return your invalid packet error.
B) after you do A, go to your blockland folder (which is usually located at C:\Program Files\Blockland)
C) find the file called "console.log"
D) use the upload feature on these forums to post that console.log.
E) after you do that, I'll look at it.