Panasonic dvd rv21 wont play copies

Hi
I recently copied movies onto DVD+R media. The copied disks played fine the first time I loaded them into the Panasonic DVD-rv21 player. Now my player just wont play the copied dvd’s… it tries to read and just stops. On a couple of them, there is a message that says the wrong DVD disks are being used. Can anyone shed some light on this?
These disks play fine on my laptop.
Thanks
lynn

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