Mail merging labels, cascading data issue

I am merging to a label template and I get an error in that the first person in the list is duplicated [so becomes record 1 and 2, i.e. Mr Smith & Mr Smith and then Mr Brown], it then completes the population of the rest of the labels only to reprint the entire list again and deleting the first records [starting with Mr Brown].

This cascading error is repeated over and over, deleting the first record, repeating the next and creates a document of 97 pages instead of 3.