How do I convert an XML DateTime in a web method

I am passing a string into a webservice that contains a date formatted as "2010-08-26T00:00:00".  this format is required by the infoPath form that passes this through XML.

When I try to convert the date into a usable date in the web method I get an error "System.FormatException: String was not recognized as a valid DateTime" when I run the application (InfoPath form).

The partial code for the web method looks like:

public string CheckDuplicates(string StartDate)
   {
     DateTime datStartDate = DateTime.Parse(StartDate);

(the error occurs on the first line of the method doing the parse)

The code works correctly if I hard code the line like:

DateTime datStartDate = DateTime.Parse("2010-08-26T00:00:00");

The application is an InfoPath form that calls this web service and passes the string, I can view the string and verify that it matches the format I indicated previously but the web method gets confused.

Is there something wrong in my code or the way I am using Parse?