nrf_log_backend_rtt.asm' for writing: No such file or directory

can't open 'J:/Projects/..../Electronics/SDK/BT840F/nRF5SDK15209412b96/nRF5_SDK_15.2.0_9412b96/examples/ble_central_and_peripheral/experimental/ble_app_att_mtu_throughput/pca10056/s140/ses/Output/ble_app_att_mtu_throughput_pca10056_s140 Release/Obj/nrf_log_backend_rtt.asm' for writing: No such file or directory

I obtained the above error trying to compile the experimental ble app, fresh from download. What else do I need to install besides the soft device?