Cannot change some cells to date format in Excel

A downloaded Bank statement refuses to allow some but not all cells to be converted to date formats.
I have 

1. tried simply to format them as dates
2. converted text to columns using both fixed width and delimiter options
3. copied the text to notebook in the hope of stripping off hidden characters
4. =DATEVALUE(A1) ->error
5. Simply justifying the numbers right
6. incantations
   

    

   
   Any thoughts? Thank you