This works for me:
A = {[5] '09/16/2007'
[2] '05/14/1996'
[3] '11/29/2010'};
dn = datenum(A(:,2), 'mm/dd/yyyy'); % Date Numbers
check = datevec(dn); % Check Conversion (Delete This Line Later)
You need to only use the second column of ‘A’ for the dates. The datenum function does not know what to do with the first column (and neither do I).