[Discuss-gnuradio] gnuradio error

[cdl]

i am using uhd model in gnuradio,usrp_sink and usrp_source to do a loopback sysrem

and i connect the usrp tx and rx withRF feeder line,when i exe the grc ,i got the output 

UHD Error:

the receiver packet handler caught an exception.

runtimeerror:usb rx6 transfer status:LIBUSB_TRANSFER_ERROR

UHD source block got error code 0xf

i wants to konw how tp solve this problem

I am using https://github.com/anastas/gr-cdma/tree/master/apps cdma_txrx.grc

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