I reported this as a bug and I'm curious if anyone else can recreate this problem:
-Create an Excel file with the header of one column labeled 'table' and export as a CSV file.
-Select the CSV file as the data source in the Data Merge pane.
At this point, nothing happens for me. Changing the column name to anything else works as expected.
I can recreate the problem. Interesting note, changing the column to Table (capital T as opposed to lowercase) will work.
For search indexing, this is the error that brought me here: The data source cannot be opened. Confirm that the file exists and that you have rights to open it, then choose the Select Data Source command again.
hopefully this helps another poor soul who spent hours trying to figure out what is going wrong
this came up just the other day, too. glad you got it sorted out.