merg replication

Hi

when want to creat a merg replication , irecieved below error message!!

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The process could not make a generation at the 'Subscriber'.
(Source: Merge Replication Provider (Agent); Error number: -2147200994)
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Cannot insert the value NULL into column 'nicknames', table 'MSmerge_genhistory'; column does not allow nulls. INSERT fails.
(Source:'Subscriber'. (Data source); Error number: 515
--------------------Check @.@.servername on all servers - I did have a situation like this.