What I said is just a disclaimer. After all, you did express intent for using it online (trades being the prime issue here), so I figured I should mention it,
not just for your benefit, but also future readers.
And now you know, bad hacks are a problem. :3
The server hack check sucks, so who knows why it blocks it.
For starters, try making it as unvanilla as possible (remove PKRuS, make unshiny etc), see if that helps.