#Name means you have that field bound and the database cannot find it.
Look at the design of your form and see whether that field needs to be bound. If it is only used for filtering, the odds are you don't need to have it bound.

Thank you for the super quick response! Turns out when I added the default value, I didn't reference it correctly. I'm no longer getting the #Name! error message but it isn't filtering either. This is where I think the timing is coming in.

Okay Monica, you know the drill. Start posting some images so we can see what's going on.

My laptop has gremlins; there wasn't an upload button Friday. Or maybe I was just braindead from trying to figure this out. The above is what it's doing. Below is what I'm going for. I'm thinking if I can make the dropdowns on the subforms follow the main form then I can hide them and the users will only see one dropdown controlling the whole thing.

*HAPPY DANCE* I decided to cut out the middleman and filter straight from the parent, but it didn't like the way I was trying to reference the filter property on the subform. Parent form is ConfirmationEmailF, and subform is LIBConfirmAdjF. I tried Forms!LIBConfirmAdjF.Filter, LIBConfirmAdjF.Form!Filter, Forms!ConfirmationEmailF!LIBConfirmAdjF.Form!Filter

Turns out somewhere along the line the Name of the subform became different from the Source Object. The only thing I can think of is I mistook Name for Caption, because it had a space in it.

The final, correct answer:
    If IsNull(Me.EmailCmb) Or Me.EmailCmb = "" Then
        Me.LIBConfirmAdjF.Form.Filter = ""
        Me.LIBConfirmAdjF.Form.FilterOn = False
    Else
        Me.LIBConfirmAdjF.Form.Filter = "EmailSubject=""" & Me.EmailCmb & """"
        Me.LIBConfirmAdjF.Form.FilterOn = True
    End If