Problem reading 6 month old Memorex 700MB 16X...

Question

I've got a TDK Cyclone 16x10x14 writer.  About 6 months ago I wrote a disk at 16X.  It wrote and worked perfectly OK. However I went to copy some of the files of the disk onto my hard disk and I get read errors on some of the files.  This happens in the TDK writer and also my DVD-Rom drive. I have since written a new disk from the same spindle pack and read it back in with no problems, from this I assume my writer is OK. I assume that the disc is somewhow reverting back to it's original state. There are no scratches etc on the disc. Is it possible for this to happen to the discs and has anyone ever had the same problem. Cheers, --Rob Singlehurst