Hi Doug
thanks for the suggestive comments!
You asking about the unique values I did awk '{ a[$1]++ } END { for (b in a) { print b } }' to see the values I have in the CHR column and turned out one "unique value" was emptiness. awk -F' ' '!length($1)' suggested a few whole lines are empty, so I deleted these from the file and did not get the error anymore.
Thanks for the help, the error message was not really directing me that way.
K