I think it is a Toast problem, your version is old - even for OS 9.1. You really should upgrade to 9.2, it's free and a little more stable.
I would first consider moving up to a later version of Toast, v5 or v6, and trying that. I note you say "formatted" when you refer to the disks you made on the 7500. There should be no formatting involved. It may have something to do with sessions. A lot of CDROM's when used with the Mac, be they burners or just players, do not like to deal with sessions. It is normal, on the Mac, to close each session and to finalize the disk.
Do the disks that you burn on the 7500, mount on the 7500? Not all burners are created equal and yours may have a weak laser by now. I'm guessing it's SCSI @ 8X (or thereabouts) but I could be wrong. Of course, it could be that your G4 AGP has the weak laser. It could also have something to do with the brand of disks that you use. I have a CDR that will NOT burn Maxell disks at all. It will also not READ and disk that has a gold surface. It burns and reads, Office Depot $20 per hundred, like a champ.
If moving up does not fix the problem, then I would consider a thumbdrive, 256MB would be good-512MB would be better, to transport your files around. At 512MB, you are very close to the max a CD will hold, around 640MB.
1. Upgrade Toast.
2. Change CD blanks.
3. Consider New Burner for both machines.
4. Firewire card for 7500 to run #3.
5. Thumbdrive when all else fails.
6. Don't use CD-R/W. Buy cheap CD-R and use them once. 20c each
Hope some of this helps
I`m taking a class at a local community college (digital audio); the instructor recommended that we use CD-RW`s to transport files from school to home, since the files are big and shouldn`t stay on the school computers.
My problem is that the CD-RW disc, formatted with Toast 4.x on my husband`s 7500 (set up for music composition with OS 9.1 and NOT going to be upgraded) on an old burner won`t mount on MY G4 AGP (running OS 10.2.8 currently, with Toast 6.11) but will show up on the eMac with OS 10.4 at school. I was able to put the files on the CD-RW at school with Toast 6.x but when I got them home, they wouldn`t mount on either the 7500 or the G4...the computers just whir a bit and kick the disc back out.. Is this a Toast problem, an OS problem or what? I still need to be able to transport these audio (AIFF) files back and forth.