The files are gcode. I've tried variations of the file extension as I understand the Marlin firmware can only support 8.3 file naming conventions. I've tried, .g .gco and *.gc
I take it that you have a similar configuration and yours is working? Are you using the "save for SD print" option in Repetier host? Which version? Are you editing the gcode generated or commenting out any lines before transfer to SD? I assumed that if the file would print from SD by triggering from Repetier over USB that that file would be correct and "good enough" for printing directly via the LCD console. However, again - no success.