Yeah, it does seems to wait for ages and then timeout. "timed out contacting server" would be a much less scarier error message than "ASN1 unexpected end of data" :-)
Anyway, glad it's not just me < phew !>
I've got support emails into Verisign and Thawte (who we got the cert from and are owned by Verisign anyway) so if I get any form of support response, I'll post it here in case anyone else hits this.
Seems like the server is back up (I used an Authenticode action with “Retry Attempts” set to 1000 and a one-minute inter-attempt delay to find out when it became available again!)