The CDX-1 reads and writes its data to formatted “high speed” CD-RW disks. A “Medium Error” indicates that either a disk is incompatible or is no longer usuable or it can mean that the drive itself needs service.
Always use “FULL” for the format mode when formatting a new “HIGH SPEED” CD-RW.
Also only use recommended brands of disks.
Avoid the following incompatible brands:
Here is a list of online resources to find compatible disks.