[Exim] Remote clamd can't access files

I've been using Exim+exiscan with ClamAV and SpamAssassin for a while
on several different systems; but all with the clamd and spamd on the
same machine. Now I need to set up one where the spamd and clamd daemons
are on a separate machine from Exim. In the Exim config, I have:

    av_scanner = clamd:clamdhost.my.domain 3310

And it appears to be contacting the daemon; but the daemon returns
the error:

    malware acl condition: clamd: ClamAV returned
    /var/spool/exim/scan/1BfQGk-0006Ao-QQ: Can't access the file ERROR

(Linebreak added) Is it possible to actually use a remote clamd
with the exiscan ACLs? If so, what am I doing wrong?



Thanks,
-Pat