Make sure to use the
-t cdrom argument.
If that doesn't help, add
-usecd 0 -ioctl.
Finally, check the CD's name as shown in windows and enter that after the
-label argument.
http://dosbox.com/wiki/MOUNT#Extra_CD_ROM_options
An alternative would be to dump an ISO or BIN/CUE image of the CD onto your hard drive and mount that using IMGMOUNT, as this tends to be more reliable and offers better overall performance (since the contents of the "CD" are in fact loaded from your hard drive).