Nostalrius Begins - Quality wow vanilla realm (1.12)

Hi, I'm a rogue level 20 trying to learn crippling poison. At first when I tried to learn it from the rogue trainer it was green but nothing happened when I clicked the Train button. Now it's greyed out, even though it says level 20 on it. The text says Requires: Level 20, Poisons(1) (the number '1' is in red).

Is this a bug or have I forgot to do something? I've restarted WoW without any effect.

Thanks for the help,
Cheers WCChamp

Having the same problem I'm now lvl 26 and still can't get it.

Figured out the problem.

Go to Mathias shaw in sw pick up the quest he gives.