>ERROR [+6210]  OpenWaveInput: Cannot open waveform file ../train/wav/sample1.flac

convert your audio to wav format (with sox)

 HCopy -A -D -T 1 -C wav_config -S codetrain.scp

C:\cygwin\HTK\htk\HCopy.exe -A -D -T 1 -C wav_config -S codetrain.scp

HTK Configuration Parameters[11]

  Module/Tool     Parameter                  Value

#                 NUMCEPS                       12

#                 CEPLIFTER                     22

#                 NUMCHANS                      26

#                 PREEMCOEF               0.970000

#                 USEHAMMING                  TRUE

#                 WINDOWSIZE         250000.000000

#                 SAVEWITHCRC                 TRUE

#                 SAVECOMPRESSED              TRUE

#                 TARGETRATE         100000.000000

#                 TARGETKIND              MFCC_0_D

#                 SOURCEFORMAT                 WAV

  ERROR [+6210]  OpenWaveInput: Cannot open waveform file ../train/wav/sample1.wav

 FATAL ERROR - Terminating program C:\cygwin\HTK\htk\HCopy.exe

Put your train folder at correct path. If you have kept train folder in voxforge folder and still getting error then try again by keeping train folder inside voxforge/auto folder. It should work.