problem when connecting a lego mindstorm nxt, error 402 not connected to a robot

[blob_]

Hello

I'm trying to connect my nxt 1.0 to my device. I have correctly paired it with my phone in the setting of my phone. 

But when I'm trying to drive my nxt trough my app, it say "error 402, not connected to a robot"

I have triyed to control my robot through an google play app, and it worked well ! but I want to code my  own app ;)

my nxt firmwar is 1.31

how to fix it ?

Thanks !

[blob_]

I have tryed to connect to it (in addition of "pairing") with a listpicker, but noe it say : "error 507, unable to connect, is the device on ? "

thanks in advance

[blob_]

SOLVED :)

how to fix error 507 :

I flashed lejos firmwar on my nxt, then I went to bluethoot client proprietes (in the designer(in app inventor)), and disabled secure connection, then I rebooted the nxt and paired it with my phone, then connected it trough my app with a listpicker block (if it give you error 507, just reboot your nxt and re-try)