Do you have a ".cue" file with that ".iso"? Most games from that generation in PlayStation and Saturn used CD audio, so many games need the cue file to play properly. If you have one, try using it instead of the iso.
Some other games could give problems in ePSXe if not properly mounted... I hate having to mount the isos (currently the only emulator that needs it on my build is ePSXe), but you could try it to see to test if the game is ok.
Some games doesn´t run on the current ePSXe version too, so you may need to take a look at version 1.6.0, which is said to be most compatible...
Sadly the consoles from that era (Saturn, PlayStation and Nintendo 64) usually have complex emulators which fail easily depending on the configuration, game, plugins, etc... If you are not into upscaling the resolution take a look at mednafen, games will work perfectly, but at the original resolution (that´s why I still use ePSXe)...