I've been burning files on DVDs for backup using finder's burning ability. after burning, when I reinsert the disc, the superdrive ejects it. I tried inserting the disc in the other G5s in the office but they keep ejecting it. But when I insert the disc in my PC at home it accepts it. I wonder what's going on.
I've had a similar experience with a CD I burned on a PC. the PC reads it just fine, but my Macs, including machines that run on Mac OS 8.1, Mac OS 9.22, and Mac OS X ejects the disc. My guess is that there is a problem with the leader track for the HFS directory (used by the Mac), and not the ISO track (used by the PC). On mac classic you could try using ISOnoHFS to prevent the Mac from reading the corrupted HFS directory, but the best thing to do is simply burn the disc again.
Burning again, results in the same problem I'm starting to think that it's the media I'm using, It's Imation DVD-R, But we don't have any other DVD brands.