[2005] ASPNET_MsgBox - works but blanks the entire screen

I have not been able to solve the problem. In my code behind I do some validity checking and if error exists I am calling the ASPNET_MsgBox sub. The code works fine but when the message box is displayed it blanks out the entire screen. When I click "OK" the web page shows again. Any idea why this is happening (work same on every computer in our company). We are using IE 7.
If TextBox2.Text <> Nothing And TextBox3.Text <> Nothing Then
If CDate(TextBox2.Text) > CDate(TextBox3.Text) Then
myError = True
Dim message As String = "'Date From' cannot be greater than 'Date To'"
< ...