Nero cd speed problem

Hello Everybody
Iam Using Nero burning rom for a long time and I was using Nero cd speed to determine the maximum overburn capacity for my Blank cds.
this program is working fine with SONY blank cds and gives me the capacity but when tring this test with Acer cds the program gives me write error from the begining of test..also with Samsung cds it gives me this error but after 4 minutes of test!!what is the problem of the program?
Thanx Very much
 
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