I went to the 'Author Area', and the first sign of problem was that the 'Submit a Revision' link had 0 papers. After that, I went to 'Author history', found the specific preprint. I noticed that the table's column 'Current Version Status' had entry 'Closed'. The preprint has 'Date of Original Submission' on September 2017.
Does anyone have any idea what is going on? I've searched in bioRxiv's site and in the web, but no clue of any rules related to closing of preprints to revision after some time since last or initial submission.