Here is how to engage the Alpha Mask on a Mac: (Antoine said that this was one of the stupidest bugs in Carrara) Render Room>File format>select the "movie" radio button>from the file format pull down menu, select "Sequenced Photoshop 2.5">open G-Buffer section At this point all of the options should be available including Mask. Once selected, you can go back and change the file format options to what you want and the Mask G-Buffer will remain selected. Mark