SQL Server 2000 Replication
That error would imply to me that there is a table layout difference between the publisher and the subscriber. Have any recent updates to the DB structure been applied to one but not the other?

You could run a DB comparison tool (something like the free edition of http://www.sqleffects.com/Articles/Product/sqlAccordInfo/aboutSqlAccordCommunityEd.html should be more than sufficient) against the two databases to check for this.

You probably shouldn't be using SQL 2000 any more - it is somewhat old and the extended support period for its last release (SP4) ended in April this year.