DFPlayer initialization fails...

[veitk]

DFPlayer initialization fails. it always tells me:

Initializing DFPlayer ... (May take 3~5 seconds) 0 Unable to begin: 1.Please recheck the connection! 2.Please insert the SD card!

i checked the wiring 3 times already... switched rx/tx ... pull down resistor is in. if i connect the ADKEY-1 to GND it plays the first mp3 on the card - so the chip an the card are working.