Sort not working in Excel

I am having a heck of a time trying to get Excel to sort by date. I've reformatted the dates (mm/dd/yyyy) but it still will not sort correctly, it's all jumbled. Also when I go to Data>Sort and then the dialogue box opens with options, I am not able to choose the column I want to sort (ie: A) and I get an error message saying the there is a missing column/row name. I've double-checked and there are no blank columns. I don't understand why Excel is not recognizing my column headings. See attached file. Any help will be appreciated. Thanks! D