Larian Studios Forums Divine Divinity (English) Help/Tips/Tricks Proof of no license

Yes, your problem is the cave letter. If you look at my link, you see what it triggers/solves.

If you can't get new speech options from Marcus/Robin/Trevor => which quests are still valid in your log book?
Kiya

[color:"yellow"]Marcus - cart - Marcus - wheel to cart - Marcus - Tingalf [/color]=> ok up to here, no harm done -

if possible: [color:"yellow"]Reload at this point, fulfill cave and letter - return to Marcus. Talk to Tingalf again - sewers/letter - Robin - Marcus - Trevor.[/color]

I think this is possible - IF you can reload.
Kiya