Hello, I have this error when I want to use useEnsembl() from BioMart :

> ensembl <- useEnsembl(biomart = "genes", dataset = "mmusculus_gene_ensembl")

Ensembl site unresponsive, trying useast mirror Error in curl::curl_fetch_memory(url, handle = handle) : Peer's Certificate issuer is not recognized.

I'm seeing something similar too. For me the error reads:

Error in curl::curl_fetch_memory(url, handle = handle) : SSL certificate problem: unable to get local issuer certificate

For now you can try forcing it to use http rather than https by setting the host argument:

ensembl <- useEnsembl(biomart = "genes", 
                      dataset = "mmusculus_gene_ensembl", 
                      host = "http://www.ensembl.org")

I see the "ensembl site unresponsive" message few times, but it eventually connects. Seems like something has changed on the Ensembl server side, so I'll contact them and try to get to the bottom of this.