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Your Pioneer changer may have a problem with either the disc you are trying in it, or the disc drive.
Try several different discs, some factory-issued rather than personally made or 'home-burned', and of several different types (e.g. if you are only trying CD-RW discs, try CD-R and CD discs from a factory too.)
You can try a cleaning kit on the drive also. CD drive cleaning kits (as opposed to CD cleaning machines) are sold for less than $10 by many outlets... if you need direction to a source for one, let me know.
And try a reset of the device, turning it Off and unplugging it from power for over 2 hours or longer, then trying it again.
After which, it is probable that the CD drive in the Pioneer changer, is having a problem, e.g. not spinning up the disc to fast enough, that requires that the Pioneer changer be serviced and/or that the CD drive in it be changed out.