Hi, I am trying to get rid of poly-a tail from my reads using bbduk.sh, however, I got a warning like WARNING! A KMER OPERATION WAS CHOSEN BUT NO KMERS WERE LOADED.

The commend I entered was (my reads are unpaired):

$ bbduk.sh  -Xmx512m -da in=Test/WT12_4_AGTACT_R1.fastq.gz out=Test/WT12_4_C.fastq.gz literal=AAAAAA ktrim=r k=23 mink=11 hdist=1

And it returns,

BBDuk version 35.92
maskMiddle was disabled because useShortKmers=true
Initial:
Memory: max=514m, free=488m, used=26m

Added 0 kmers; time:    0.012 seconds.
Memory: max=514m, free=469m, used=45m

******  WARNING! A KMER OPERATION WAS CHOSEN BUT NO KMERS WERE LOADED.  ******
******  PLEASE ENSURE K IS LESS THAN OR EQUAL TO REF SEQUENCE LENGTHS.  ******

Input is being processed as unpaired
Started output streams: 0.077 seconds.
Processing time:                8.404 seconds.

Input:                          1948334 reads           167556724 bases.
KTrimmed:                       0 reads (0.00%)         0 bases (0.00%)
Result:                         1948334 reads (100.00%)         167556724 bases (100.00%)

Time:                           8.500 seconds.
Reads Processed:       1948k    229.20k reads/sec
Bases Processed:        167m    19.71m bases/sec

I checked my sequence and there was no read with less than k nucleotides. I also reduced k value and it didn't work. Could you help me out? Many thanks.