yeah yeah, well i was going mad with a scene set up that had seemingly worked then didnt
I trawled the net and although this problem (internal exception, scene cleanup exception) seems to be common theres no accepted cure, aside from what ive done. At one point i printed out the mental ray output window but that got to 140 pages and i gave up.
I do remember someone asking me what render settings i used and when i have time i'll print them up, although i basically followed the FG/GI tutorial on Interstation, which is a good tut, gives u an idea about what does what. So my current set up is fake GI dome with a keylight but its all coming out lovely now. I did bump up the AA last night on a test and it only adds another 3 mins to the render (about 12 mins with photon emmision and the rest of it) .I havnt got a clue what that will mean when i get the rest of the geo imported but i was hitting 30+ mins a render on the old set up.
ah well, good things come to those that wait