Problem when composing a new email

Hi, I'm facing the following problem when composing a new email. Once I filled all the form I hit 'Send Email' and then a warning appears on top of the page saying 'You must specify a valid date'. This don't happen when replying to an existing email from the INBOX. I've been looking through the code but I don't exactly know where does the warning gets triggered. It seems somehow the form is not validated properly or the date value is not passed to the module in order to process the mail composition.