Thanks. Unfortunately that doesn't seem to make any difference either with WMP or MPC. I tried clicking on the .ifo file (from the HDD not the emulated drive) and WMP was happy playing that. I have another .iso file that happily plays however, if I use Opti-Drive Control to look at the physical drive/disk it tells me that the .iso that won't play is a CD and the one that will play is a DVD-ROM. This is despite Windows explorer telling me that they are both DVD-ROM drives. The size of the .iso that won't play is just 140Mb, if that make any difference.