> All mame versions below 77u1 can't run them because they don't understand the
> new format. That's why mame shows errors.

Ok - but the above is why I think some sort of message would have been generated. I'm sure there will be peeps out there who will blindly download the 'new' CHD's, then wonder why their 'old' MAME won't run them.

Is there some sort of message you can put in there, stating that they need to 'update' their MAME version to run the new CHD's? Otherwise you'll have peeps who aren't as experienced with MAME as I am, asking roughly why the CHD's won't work. :-)