Input string was not in a correct format #2

double temp;
temp = (double)Convert.ToDouble("1234.5678");

Hey Lads and Ladies, I can't for the life of me figure out why the above line isn't working. The above line gives me a runtime error that says;

An unhandled exception of type System.FormatException occurred in mscorlib.dll

Additional information: Input string was not in a correct format.