Two Dataset companied merge queries using left join ,,it type dataset did't work scheduled refresh.

I getting data from 2 various database ,Create dataset as separatly A and B.. i need B table columns in A table. so i used merge Queries with left join in references values.reports are working fine but did'nt working for 'Sheduled refresh'

ther showing error is(There was an error when processing the data in the dataset)---Anyone have a better idea for this issue.?