1.8 works, but older versions always crash

Put the summary of the bug you're having here

What I expected to happen was...:
the play.timolia.de server should work with an 1.7 version, because it has not yet been updated to 1.8

What actually happened was...:
when i tried to join the server, minecraft crashed.

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...