Hi Mike,
Thank you for your reply !
Surely I should give you more information :
I downloaded sequences from Japan for the Insecta class on the BOLD platform.
I removed the sequences which didn't correspond to the COI-5P on both the taxa and the sequences files and renamed the duplicates.
Then, I proceeded as stipulated in the tutorial "Building a COI database from BOLD references".
Setting the --p-rank-handles as 'disable' leads to the same error message as before.
Sending you my files right now ! Thank you so much !
Ander