Date Field problem

I've a add page where a user can input a date.
The Edit As setting is Simple Editbox with datepicker.

The Date Format is DD-MM-YYYY Dutch (Standard).
When an user inputs 01-01-2007 he can add a record.

When an user inputs 01012007 he gets an http 500 error.
The error is:

Microsoft VBScript runtime error '800a0006'

Overflow: 'cint'
How can I solve this error?