MKR1400 AT+CPIN? Problem

hello, tried examples of mkrgsm library , have same problem each time.
the modem not respond correctly @ + cpin?
i receive error systematically after at+cpin?
my sim card not have pin, used #define secret_pinnumber     "".
i tried gsmaccess.begin(null).
the sim card works in sim900.
i have 2000 mah lipo battery full loaded.
the blink example works correctly (led on pin 6 blink).
the testmodem example works correctly, receive modem imei.
the gsmwebclient stops @ gsmaccess.begin.
in debug mode (gsm gsmaccess(true) can read :
at
ok
at+ipr=921600
ok
at+upsv=3
ok
at+cpin?
error
at+cpin?
error
at+cpin?
error...........

hi @innometrix,

would possible test sim (maybe 1 cellphone)?

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