The answer was to rename one of the columns called Name. Eg.
select Applications.Name as App , Computers.Name from Computers left join Applications on Applications.ComputerId=Computers.ComputerID
The message that was coming up was offering to submit a bug report, but if I looked closer, in among the diagnostic information it says "Error : A column named 'Name' already belongs to this DataTable."
Strange way to offer diagnostic information.