Are you using both the USB and other SPDIF inputs like the Coax or Optical? Try using only the USB. There's a bug where if both USB and SPDIF are used at the same time, the remote stops functioning.
But switching to the Player mode and then playing songs from the SD Card will then cut off the USB SPDIF input and it no longer functions until I power cycle the HM-901 player, so mode switching between the player is essentially useless right now.
Lots of bugs to fix, but it does sound glorious when using USB input.