Ok, I have uninstalled and reinstalled new Nvidia drivers, reinstalled NET framework, C++2008 and finally reinstalled Poser8. It works for now. It seems that Poser CAN'T export movie with transparent background at all.(????) At least I have managed to export series of PNG images with transparent backruond (by turning off OpenGL mode) instead of AVI file. I will have to combine them into one sequence in Vegas. It seem that it's only solution. Pitty...