depends - what is M12S and M12F? If they are date time pickers, then you should be using M12S.Value and M12F.Value ... because that's what you're really after and that will return the value typed correctly as a Date... I think what had been causing the issue was that by default the DTP will return the .ToString which is just that, a string, which isn't what you really want. You want to keep it as a Date.

This concerns me though...
and it should have been 20131216.
or did you mean 2013-12-16?

-tg