I am assuming the Arma II Beta patch. DayZ Alpha is reversable but the Arma II one isnt.
After installing the Arma II Beta (it is build 94876) most servers are not enterable due to being a different version. The reason I can see is that all previous Arma II Beta patches are 1.60.**.*** , this new one is 188.8.131.526 , the 1.61 part seems to throw the game off.
EDIT: Actually, hold off the 184.108.40.206 - it's experimental, broken on purpose (Zombies no longer despawn on logout, creating excessive Zombie spawns), says please test this if you don't mind losing your gear as can bug to death on entering, though a chance your body with gear will spawn next to you - camo/ghillie is meant to be working but if you lost it by logging in during 1.7.2 you won't regain it.
Still can't 100% confirm the Arma II Beta part, all I notice is that with 220.127.116.11 and 94876 I can't select anything prior to 94876.. The same if I have 1.7.2 or 18.104.22.168 with this Arma II Beta patch, only shows the latest 22.214.171.124 servers as enterable, all others have the red X next to them and can't join.
And for my final edit - 126.96.36.199 will be released today says Rocket http://dayzmod.com/forum/index.php?/topic/28091-build-172-rolling-update/page__st__1360#entry298554