Why Can't I Burn 48X Memorex CD-R'S?

Hi, I am backing up data files onto CD-R’s using 2 year old TDK VELO CD 12/10/32 and Roxio Easy CD Creator Basic. Everything worked fine until I used up my last TDK 24x CD-Rs. Now I am trying to use Memorex 48x CD-R’'S and I cannot get them to work, they slow down to burning at 1x and then I get “cannot read” error messages.
I opened several different boxes of the Memorex CD’s in case first was defective, no difference. I downloaded latest version of Roxio Creator Basic program, again no difference. If it would solve the problem, I can reinstall Nero 5.5 (I have both) but is that really the problem?
Thanks in Advance

AMD 1800XP
512 MG Ram
MSI board

Have you updated the drive to latest firmware.

Can you post the drives current firmware.

There are 2 versions 121032A and a 121032. Be careful to select the right firmware.