VS 2008 Make ListViewSort And Dates?

I'm implementing a Listview sorting class into my application and it is working well for String, Integer and DateTime column types. However, I cannot get it to work for columns containing ONLY a date.I get an error saying "string was not recognized as a valid datetime"The date format in the column is dd/mm/yyyy (and the ListviewColumn type is string).This is the code that generates the error

vb
Dim date1 As Date
Dim date2 As Date

[code].....