USB boot error can't open /dev/sr0 no medium found

[born]

HI,all.

      my OS is ubuntu 9.10(for desktop)
     I use remastersys to make a custom ubuntu ISO. Install the custom
ubuntu ISO on the USB key.
The USB key boot a little slow.I found it spend much time on this error

"init: /line 1 can't open /dev/sr0  no medium found"

I could use the USB key to login into the system.
could anyone help me to make it boot faster? Thanks anyway!
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