Field pin code employs some characters that can not be erased. Darkcoin pool.
What to do?
Would you clarify what is the problem?
Do you want to reset your PIN number? or you mean PIN edit box is not editable.
If you want to reset PIN, then you can do it at "Edit Account" page.
If you can't edit PIN edit box, then try to use modern web browser like IE8+, Chrome, Firefox