I had the same...pls edit /etc/clamav-unofficial-sigs/master.conf
# Custom Command Paths, these are detected with the which command when not set
clamscan_bin="/usr/bin/clamdscan"
#curl_bin="/usr/bin/curl"
#gpg_bin="/usr/bin/gpg"
#rsync_bin="/usr/bin/rsync"
#tar_bin="/usr/bin/tar"
#uname_bin="/usr/bin/uname"
#wget_bin="/usr/bin/wget"
# Custom Command Paths, these are detected with the which command when not set
clamscan_bin="/usr/bin/clamdscan"
#curl_bin="/usr/bin/curl"
#gpg_bin="/usr/bin/gpg"
#rsync_bin="/usr/bin/rsync"
#tar_bin="/usr/bin/tar"
#uname_bin="/usr/bin/uname"
#wget_bin="/usr/bin/wget"