You will need to have a distinct set of ActivityTagID in your PivotColumnHeaders. Try adding the group by ActivityTagID in your query as such:

DECLARE @PivotColumnHeaders VARCHAR(MAX)

SELECT @PivotColumnHeaders =

COALESCE(

@PivotColumnHeaders + ',[' + cast([ActivityTagID] as varchar) + ']',

'[' + cast([ActivityTagID] as varchar)+ ']'

)

FROM dbo.ConversionsTest

GROUP BY ActivityTagID

http://www.ingenioussql.com/2013/02/06/dynamic-t-sql-pivot/

Thanks,

Dave