I have a custom list (clicked together on the portal site, so no custom templates) in which attachments were disabled and afterwards re-enabled. The "Attach file" action menu item does however not re-appear on the New/Edit forms. No other customizations are done by the key-user since they have no access to SharePoint Designer or Visual Studio. Is there a way to get this functionality working again?
I recently picked up this project again (since it just had to be finished after all :)), and I found out what caused the attach file button to disappear when I recreated the list they left me from scratch.
If you try to use a calculated field with a reference to [Today] or [Me] you get a nasty error message which prevents you from making the column.
Calculated columns cannot contain volatile functions like Today and Me
Now if you think you're smart, you can create a column Today, enter the formula in the calculated field and remove the column Today. Tadah, it 'works'. Now go try and make a new item and the upload attachment button might be gone.