mothur removes my seq data

Commands in mothur
1

When I go to the step screen.seqs:
mothur > screen.seqs(fasta=stability1.trim.contigs.good.unique.align, count=stability1.trim.contigs.good.count_table, summary=stability1.trim.contigs.good.unique.summary, start=1968, end=11550, maxhomop=8)

It comes back:

Removing group: C_19-4 because all sequences have been removed.

Removing group: C_19pl6 because all sequences have been removed.

Anyone can suggest what is going on?

Thank you.

2

When all the sequences are removed from a group in the count table mothur reports it to you.

3

Thank you for your replying. Can you tell me why it is. How do we find out a way to fix it?