Hey, I seem to have hit a wall in the main quest - my journal says I should report back to Caius about the Dissident priests, but there is no option to talk to Caius, he just keeps saying I should talk with Nibani Maesa, which I have done... Any help would be greatly appreciated.

Have you tried the 'Order' topic when talking to http://www.uesp.net/wiki/Morrowind:Meet_Sul-Matuul?

Also make sure that you have a journal update saying that you should report back to Caius.

Also, did Sul-Matuul send you on a quest?

This is where I'm at with the journal entry:

The wise women know that some Nerevarine prophecies have been lost. But the Dissident Priests of the Temple study the Ashlander Nerevarine prophecies, and record them in books. Perhaps the lost prophecies can be found there. Nibani Maesa has asked me to go to the Dissident Priests, get them to show me the books, and to tell her what I find there. This sounds like something to mention to Caius. Maybe he'll know how to contact the Dissident Priests.

Except, I can't talk to Caius about them - his orders tell me to go to the Urshilaku Camp... which I've done and did the quest for the bow, and spoken to the wise woman about the prophecies. There's no option to talk to him about Dissident Priests either...

If you have such a journal entry then go back and talk to Caius via the 'Order' topic.

Did she give you copies of The Stranger and The Seven Visions?

I've done this, and his order topic just tells me to go to the camp.

Hmm... Have you tried any Nerevarine related topics or perhaps the Ashlanders topic?

I'll have a look Hmm, it doesn't appear so. I'll return to the camp and see if she'll give me them

Also check your factions and see if you're already a member of the Ashlanders, because if you're not a Clanfriend then you haven't done what Sul-Matuul asked you to do.

I'm on the second to last one on this list:

http://www.uesp.net/wiki/Morrowind:Meet_Sul-Matuul

I'm also a clanfriend of the Ashlanders.

You must have this line in your journal before you can talk to Caius via the 'Order' topic...

...and that line should be found in the journal entry after this journal entry in post #4.

If you exhaust all of your conversation options with Nibani and still don't get the entry that Leonardo quoted, AND if your playing on a pc, console journal A2_1_MeetSulMatuul 60. That won't give you the two books though. They can be added with player->additem if you need them. Do NOT save until all is straight with Caius.