Are you using the correct Subform notation to set the RecordSource?

Value From A Form

Forms!FormName!SubformName.Form.RecordSource

There's the problem. I was leaving off the Form. before the RecordSource.  Thank you SO much!

Thanks for the link! I just now noticed it. :)

I'm still getting an error saying Access can't find the field "AccountTransactionF"

   WhereStr = ""
    If AccountSearch <> "" Then
         WhereStr = Forms!Budget!AccountTransactionF.Form.Account Like "" * " & AccountSearch & " * """"
   End If

You said the search fields were on the main form so the code including the SQL statement is also on the main form.
You should only need that notation for the RecordSource of the Subform.

WhereStr = WhereStr & "Account Like ""*" & AccountSearch & "*""""

If this doesn't work please upload some screenshots.

The SQL2 displays correctly "SELECT * FROM Budget_Q WHERE account LIKE "*0222*", but it still won't filter my subform. This is my code.  I even deleted my Account in the subform because it was a combo box, and just put in the Account field, and it still won't work. I created a new form that doesn't have a subform, and it works in it. I've used it for years filtering the subform with the search fileds and a query box, but really wanted to get this to work. Thanks again for looking at my work.

Private Sub RequeryForm()
    Dim SQL As String
    Dim WhereStr As String
    
    WhereStr = ""
    If AccountSearch <> "" Then
        WhereStr = "account LIKE ""*" & AccountSearch & "*"""
    End If
    
    SQL = "SELECT * FROM Budget_Q"
    
    If WhereStr <> "" Then
        SQL = SQL & " WHERE " & WhereStr
    End If
    
    Me.RecordSource = SQL
    SQL2 = SQL
End Sub

Private Sub SetDefaults()
    AccountSearch = "-"
End Sub

Private Sub AccountSearch_AfterUpdate()
    RequeryForm
End

Never mind! I figured it out. I had to use Me.AccountTransactionF.Form.Recordsource = SQL and then it worked!