I had the old version on server (that from sme7contribs)
I have done
yum upgrade smeserver-sysmon --enablerepo=smecontribs
and then
service sysmon stop
rm /var/lib/rrd/*.rrd
mv /var/lib/rrd/backup/*.rrd /var/lib/rrd/
service sysmon start
and everything is fine
The upgrade procedure "on the fly" is Ok , ether