More info please.
Do you have real mode drivers for the CD in the Autoexec.bat and config.sys files in your root directory, or is it running the Virtual Win driver?
Does this happen all the time, or just occasionally?
Have you disabled the auto detection of all drives other than your Hard Drive (s) in the BIOS?
What type/brand of CD ROM is it?
If it worked OK initially then started playing up, what software/hardware did you load/change immediately prior to the fault?
Have you run sfc.exe (from the 'run' on the start menu)? This may pick up the odd changed file in WIN that may be having a hernia. Some software loads its own files, overwriting the WIN files, and this can cause problems, although this is a hardware fault and not likely to be the cause.
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When all else fails, read the manual!