'New' cannot be used on an interface > Dim dt As New DataTable("ID") <- works on some vb forms but not on other

hi,
i've got 2 vb forms and i cannot for the love of me figure out what the difference between them are.

Dim dt As New DataTable("ID")

works on my 1 form, but not on some of the other forms
it give the ERROR : 'New' cannot be used on an interface

i searched for word interface on the page, but didnt find it.
i can copy the exact code to another vb.net page and it will work there.

pls help.
thanks!