Chat's pretty unreliable at the best of times. Make sure that you have chat enabled (tools > options > chat).
If you see a smiley in the Chat column, means that the other host has chat enabled & you at least have a chance of chat working. Lots of people have their LW running while they're not in front of the computer though... in that case they won't answer your chat!

Just keep trying, it's trial & error really plus a bit of luck. There's a sticky at the top of this section about Bitzi, direct connect/browse/chat... have a look at that