Here's the contact.aspx page from BE 1.5.
If you use the contact.aspx page from 1.5, you'll probably need to do a search and replace. You'd want to replace
BlogEngine.$ with just $
The main thing to change is in the older contact.aspx, it has code that looks similar to:
if ($('<%=txtAttachment.ClientID %>').value.length > 0)
This is basically the same code you posted two posts ago. If you're not going to use attachments, you can just remove those two lines of code from your existing contact.aspx page, and that should eliminate the JS error.