rename.seqs problem



I’m analysing a big dataset and had to divide it in 3 pieces in order to do preclustering and chimera search (when doing all at once, mothur crashes). I thought it would be kind of no bid deal to merge the parts afterwards, but apparently it is. I need to rename the seqs in order to run merge.count, but when I try to rename (rename.seqs(fasta=column_exp_part1.trim.contigs.good.unique.good.filter.unique.pick.precluster.pick.fasta, count=column_exp_part1.trim.contigs.good.unique.good.filter.unique.pick.precluster.denovo.vsearch.pick.count_table)
). I get [ERROR]: M00485_393_000000000-BCVGY_1_1103_14203_18821 is not in your file, please correct.

However, the sequence in question is in my fasta and count file, and when I try summary.seqs (summary.seqs(fasta=column_exp_part1.trim.contigs.good.unique.good.filter.unique.pick.precluster.pick.fasta, count=column_exp_part1.trim.contigs.good.unique.good.filter.unique.pick.precluster.denovo.vsearch.pick.count_table)
), that runs without a problem with the files in question. Please help, what am I missing here?

Thanks a lot!!!