I received the error 'The string was not recognized as a valid DateTime. There is an unknown word starting at index 17' on a server when trying to convert a Date and Time string to a DateTime, but I had no such error in development or testing.

The string in question was "20 MAY 2019 10:37a.m.".

I found that the problem was with the AM and PM designators on the server, they were set in the format of “AM” but all other servers where set to “a.m.”.

I could have logged a job for someone to change the setting on the server, but I wasn’t convinced that I wouldn’t get the problem when deploying to a different production server, so I decided to build the fix into the solution.

The Fix

The fix is to dynamically change the AM and PM designators in the culture.

Here is how I did it…

protected DateTime CombineDatetime(string date, string time)
{
	// format for parsing
	string dateTime = date + " " + time;
	CultureInfo culture = CultureInfo.CreateSpecificCulture("en-NZ"); // or whatever you have
	DateTimeStyles styles = DateTimeStyles.None;

	// set the AM and PM designators based on the input style
	if (dateTime.ToLower().Contains("a.m.") || dateTime.ToLower().Contains("p.m."))
	{
		culture.DateTimeFormat.AMDesignator = "a.m.";
		culture.DateTimeFormat.PMDesignator = "p.m.";
	}
	else if (dateTime.ToLower().Contains("am") || dateTime.ToLower().Contains("pm"))
	{
		culture.DateTimeFormat.AMDesignator = "AM";
		culture.DateTimeFormat.PMDesignator = "PM";
	}
	else
	{
		// must be 24 hour, so do nothing
	}

	DateTime tempDate;
	if (!DateTime.TryParse(dateTime, culture, styles, out tempDate))
	{ // this should never happen
		return DateTime.MinValue;
	}
	return tempDate;
}