Summarize VAR Calculated Table

Hello, 

I'm struggling with DAX and especifically with how the Summarize function works. If you try to summarize a Calculated Table that previously was set in a VAR, you cannot use the columns for do any operation, let me put below an example:

DAX code (Example) 

EVALUATE

VAR Sales_bycategory = CALCULATETABLE(Sales, "Date", Sales[Date], "Prodcat", Sales[Product category], "UnitsSold", Sales[Units Sold]) 

VAR Summary_category = SUMMARIZE(Sales_bycategory, [Prodcat], "TotalunitsSold", SUM(Sales_bycategory[UnitsSold])) 

RETURN Summary_category 

You would expect that the Summarize identifies the table and column to do the grouping, apparently the Summarize function do not recognice Columns from a calculates table wrapped in a Variable. 

Any idea? 

Thanks!