hmm... that is not a good sign.
It seems like there might be some kind of hardware problem then.
Has that SD-card worked before, on the printer?
Can you read the sd-card on your computer?
Is it formatted as FAT?
Is the SD-card 2Gb or bigger?
Can you wiggle the SD-card, to see if it gets a better position in the card-reader slot?
Could you clean up your Arduino install?
This means removing or renaming the (windows-user)\documents\Arduino folder
And likewise renaming/removing folders in:
-- (windows-user)\AppData\Local
-- (windows-user)\AppData\Roaming
These two locations might have folders named Arduino or Arduino15
Please note that "AppData" folder is a hidden/system folder, so you need to add this visibility in windows explorer to see this folder.
Then try the SD_listfiles test-sketch again.
It seems like there might be some kind of hardware problem then.
Has that SD-card worked before, on the printer?
Can you read the sd-card on your computer?
Is it formatted as FAT?
Is the SD-card 2Gb or bigger?
Can you wiggle the SD-card, to see if it gets a better position in the card-reader slot?
Could you clean up your Arduino install?
This means removing or renaming the (windows-user)\documents\Arduino folder
And likewise renaming/removing folders in:
-- (windows-user)\AppData\Local
-- (windows-user)\AppData\Roaming
These two locations might have folders named Arduino or Arduino15
Please note that "AppData" folder is a hidden/system folder, so you need to add this visibility in windows explorer to see this folder.
Then try the SD_listfiles test-sketch again.