https://devzone.nordicsemi.com/f/nordic-q-a/62690/how-to-upload-hex-file-in-nrf51-sensor-tag-using-nrf52840-dki was trying to upload the hex file in nrf51 sensor tag using nrf52840 DK but when i connect board with nrf connect desktop its saw me error like this &quot;ERROR Could not fetch memory size of target devkit: Error: Error occured when get library info. Errorcodeen-USTelligent Community 13Thu, 18 Jun 2020 04:43:12 GMThttps://devzone.nordicsemi.com/thread/255656?ContentTypeID=1Thu, 18 Jun 2020 04:43:12 GMT137ad170-7792-4731-bb38-c0d22fbe4515:9238ecfa-84bc-4389-bb7d-bc109feaac27vivek khatri<p>thank you.</p> <p>it&#39;s working now.</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/255536?ContentTypeID=1Wed, 17 Jun 2020 12:43:20 GMT137ad170-7792-4731-bb38-c0d22fbe4515:6bc46c26-df1c-4dfe-a8fc-51177b02716dSimonr<p>Hi</p> <p>The nRF52840 DK supports programming and debugging external boards with nRF51 SoCs, so there should not be a problem doing so. The error you are seeing is generally caused by an error in your setup. If your custom board does not have a 10-pin debug header, please make sure that the device is connected to the DK as shown in the picture below.</p> <p><img src="https://devzone.nordicsemi.com/resized-image/__size/320x240/__key/support-attachments/beef5d1b77644c448dabff31668f3a47-1a396bdb23c04537adf1cf567a56f2cd/ext_5F00_52DK.png" alt=" " /></p> <p>Best regards,</p> <p>Simon</p><div style="clear:both;"></div>