I've been playing Minecraft for years, very good in and out ofgame, coding bukkit plugins, making minecraft mod, etc, and I found got about FORCE UPDATE xD I went to delete the version file in the bin folder
I already answered his post back on the front page. We have since moved on and he found it. You're a bit late to the party bro.
I forgot that if you griefed you would be banned and i placed signs saying i griefed for a joke! the next day i realized i shouldnt have done it, so i tryed to join to put it back, but i was banned! please unban me.
The fact that 1.5.2 isn't (or should I say wasn't) compatible with 1.5.1 means that there was either: 1. a significant change in some .class files (which isn't the case), or 2. many patches were written to the new version (which is closest to the case)