You might be able to log in if StatusEffectHUD is disabled, because you weren't kicked by the server. Most likely this will cause a different crashDoubtful, it probably kicks the player on the first tick after they're finished logging on, so the timer never gets a chance to decrement.
I can confirm that a similar issue happens on Monster 1.1.2, but it doesn't look like it's still Reactorcraft causing it.
Mod Pack: Monster 1.1.2
Mod & Version: Thaumcraft 4.1.0g
Pastebin link to crash log: Server: http://pastebin.com/Ukmcj5Dv ; Client: http://pastebin.com/uSYb8kBB
Whats the bug? Consuming Thaumcraft mana beans has a chance of placing an unknown status effect on the player that immediately crashes their client. All subsequent login attempts will continue to crash the client.
Can it be repeated? Yes.
Known Fix: Don't eat the mana beans. To fix an afflicted player, delete their player.dat file.