SSRS returned data type not valid for the aggregate function

Question

I am making a SSRS, when executing the query

SELECT Brand.[KeyOffer],
   COALESCE(SUM([Key Offer].Revenue),0) as Revenue
FROM [Brand Key Offer] Brand
LEFT JOIN [Key Offer] ON Brand.Keyoffer = [Key Offer].[Key Offer] AND [Key Offer].[Date] = '7/05/2017'
WHERE Brand.[Brand] = 'SMART'
GROUP BY [Brand].[KeyOffer]
ORDER BY [Revenue] DESC

But when I preview the reprot, I get this warning message.

Warning     [rsAggregateOfInvalidExpressionDataType] The Value expression for the textrun ‘Textbox21.Paragraphs[0].TextRuns[0]’ uses an aggregate function with an expression that returned a data type not valid for the aggregate function.       c:\users\t-aordiz\documents\visual studio 2015\Projects\TelemarketingRS\TelemarketingRS\Telemarketing Revenue.rdl   0   

Ive been to a lot of topics but cant seem to find a way to solve this problem.

Answer 1

The same happened to me when I tried to change an output's datatype from datetime to varchar.

Try to delete the file YourReportFile.rdl.data and preview again. It worked for me in VS2015.