Upgrade config from 2.4.49 to 2.5.11 is failing.

Current Openldap 2.4.49 is working fine with syncprov configuration. Planing to upgrade to recent versions. Took backup of system using slapcat.

Upgraded the dev server to 2.5.11. Now when trying to import config using slapadd. It is failing with following error.

overlay_config(): overlay "syncprov" already in list slapadd: could not add entry dn="olcOverlay={1}syncprov,olcDatabase={0}config,cn=config" (line=1900): slapadd shutdown: initiated slapadd destroy: freeing system resources. syncinfo_free: rid=100

Any help or tip?

Thanks Farooq