Never noticed that different cultures write their data and time in different formats? Although the format you use is valid in most Western European countries it is rubbish in the United States.
To overcome this problem, you can ask the system for the current date and time format:
var currentCulture = System.Globalization.CultureInfor.CurrentCulture
IFormatProvider dateTimeFormat = currentCulture.DateTimeFormat;
string dateTxt = @"13/7/2015";
System.DateTime myDate = System.DateTime.Parse(dateTxt, dateTimeFormat);
That should do the trick if your computer has the correct culture.
If you want to be able to understand a lot of cultures, don't ask for the current culture but use one of the constructors of System.Globalization.CultureInfo
Not wise, because does 1/3/2015 mean March 1st, or January 3rd?