Here's the post explaining the posting restrictions.

Are you getting any error messages when you use that macro? What do you have targeted, and what does your target have targeted? Can you cast Cure without using a macro?

The only reasons I know of for that macro to not work at all would be your target's target being either out of range or out of your line of sight. If you don't have a target (and thus no <tt>) or if your target doesn't have a target, it should fail that line and fall to the second to self-cast. If your target's target is hostile or otherwise uncurable, it should self-cure via the first line, then fail the second line since you're already casting.

Well, that being in some situation that won't let you cast Cure (out of mana, silenced/stun/slept, not having access to the skill, etc.).