https://devzone.nordicsemi.com/f/nordic-q-a/75548/basic-sample-when-using-nrf51-dk-boardHello support team Devzone. I am new member and i have a nRF51 DK board. I try to create hex file for my nRF 51 DK board on the website : Mbed Compiler when compiler 1 error has occurred : Error: Undefined symbol assert_nrf_callback (referred fromen-USTelligent Community 13Tue, 25 May 2021 08:57:14 GMThttps://devzone.nordicsemi.com/thread/311366?ContentTypeID=1Tue, 25 May 2021 08:57:14 GMT137ad170-7792-4731-bb38-c0d22fbe4515:2350643f-1867-4f7c-9440-459e41e0d7e8awneil[quote userid="104679" url="~/f/nordic-q-a/75548/basic-sample-when-using-nrf51-dk-board"]I am new member&nbsp; and i have a nRF51 DK board[/quote] <p>Any particular reason for starting with that? It is rather old...</p> <p>Note that&nbsp; nRF51 are not recommended for new BLE designs:</p> <p><a href="https://devzone.nordicsemi.com/f/nordic-q-a/42960/status-of-nrf51-products/169728#169728">https://devzone.nordicsemi.com/f/nordic-q-a/42960/status-of-nrf51-products/169728#169728</a>&nbsp;- and note that&#39;s over 2 years ago now!</p> <p></p> [quote userid="104679" url="~/f/nordic-q-a/75548/basic-sample-when-using-nrf51-dk-board"]I try to create hex file for my nRF 51 DK board on the website :&nbsp;<a href="https://ide.mbed.com/">Mbed Compiler</a>[/quote] <p>mbed is an independent 3rd party; AFAIK, mbed does not use the Nordic SDK - so you need to go to mbed for support with that</p> <p><a href="https://forums.mbed.com/">https://forums.mbed.com/</a></p><div style="clear:both;"></div>