OSX Panther ejecting imation DVD-R

[iMacAlien]

I just got Toast 6 Titanium, and upon inserting a blank "imation" DVD-R I find that it won't mount the disc. It just keeps spitting it out. If I insert the blank "Apple" DVD-R that came with the iMac it mounts it just fine. I've also been having problems with CD-R's as well. Before I upgraded to Panther, when I burned a playlist in iTunes, the generic blank disc image on the desktop would disappear, then upon completeion of the burn a new disc image would appear with whatever I titled it. Under Panther, upon completeion of a burned CD-R I end up with 2 disc images on my desktop...one of the blank CD-R, and one of the new burned CD-R. If I drag the burned one to the trash, it ejects as it should, but the blank CD-R image remains. If I try & drag that to the trash, it asks if I want to burn it. Could there be something wrong with the disc drive? I once had to manually eject a disc by opening the door, and pushing on the little white tab under the superdrive. I'm wondering if doing this might have damaged the drive. It seems to work fine otherwise.

TIA for any advise,
-Jeff

PS-Running OS-X Panther 10.3.2 on a 17" flat panel iMac 800 SuperDrive