Help: Philips Multi-speed CD-R media

[dxg0072001]

Hi, i bought a pack of 10 philips multi-speed cd-r discs. I noticed that my NERO burning rom 6 sometimes detects the disc inserted as CD-R, yet it refuses to burn. I have about 4 such discs which are giving problems. I'm using Win 98 and Iomega ATAPI internal 48x24x48 drive. Can anyone comment on this problem? The rest of my discs are working fine, except for these four. Guess I'll be buying sony media next time....