Recurring bug, anyone else seeing...

I've several games where I'm at war and want to talk to end it but the diplomacy screen will not come up. Anyone else experiencing this? Is there a fix for it?

Post a savegame so others can see what is going on. I haven't seen this, other than the "refuses to talk" screen you get sometimes.

Also, you are not able/allowed to negotiate with vassals - ask the master to end the war.

I have noticed a refuse to talk length variance. Some AIs seem to talk very fast if they're getting beat down, while others seem to take FOREVER, even if you've taken 3/4 of their cities already they still won't talk...I've had an AI refuse to talk until near-death (well, it had 6 or 7 cities and I took 5, but it was hardly a bad situation for me as I took them in like 7 or 8 turns or something - a time where you'd just kill the target but still amusing that they'd not talk).

Must be coded to vary by AI or situation or somethings.

It's the leaders' RefuseToTalkWarTreshold from the xml (5 DeGaulle ... 12 Sitting Bull) doubled if they DoW'd you and scaled for war success ratio (if you have more than 2* their war success it can be reduced down to 20%). There is no scaling for game speed.
So minimum: You DoW DeGaulle and annihilate his SoD + take cities without losing a single unit --> 1 turn
Maximum: Sitting Bull declares war on you and you aren't winning --> 24 turns.