Brewology

I can't figure this out. I can't launch ISO's from IRshell, it always tells me that there is no UMD inserted, even when I have the UMD mode to no umd required!

Make Sure it is on the M33 driver rather then the Sony NP9660
(assuming your PSP has m33 CFW on it),
Also there are sometimes if you have a custom theme with a custom boots,
Make Sure that "Skip Sony Logo" on your recovery menu is DISABLED

If this does not Help Any, Post back
and Please next provide
•What Type of CFW and Version , i.e. 5.00 m33-2
•What Version of IRShell you have