Attachments in sharepoint custom list forms

Attachments usually work fine for a custom New Item form created from Sharepoint Designer, but if you create a custom Edit Item form, you'll get the javascript error "This form was customized not working with attachment." when you click the attachments button.

Here's the Microsoft fix: http://support.microsoft.com/kb/953271

Basically the attachment button launches a javascript function UploadAttachment() that hides a span with id "part" which is usually the body of the form and shows just the attachment div. If you look at your custom New form you can see how it works.