Ritek 4x only writing at 2x
 

Has anyone experienced 4x Ritek writing at 2x?
I have win2k, one of the latest versions of nero, sony dru500A firmware 2.0E.
I purchased a couple of hundred clonecd ( Ritek 4x) dvd-r's as they was a special on.
However when I put blank in tray, Nero/recordnow gives me the option to burn at 4x.
It looks at says its writing at 4x(15min) but it takes the time of a 2x (30min)
I bought 300 and only 60 of say 160 are actually writing at 4x.
Anybody any idea's on what the issue is?
Faulty discs maybe?

Any help appreciated.
Scott.

Look here

thanks... alot of reading to do now:)