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Private Sub Command8_Click()
    Dim cmdTableName As String
    Dim selectedTable As String
    ' Get the table name from the text box
   selectedTable = Me.Text118.Value
    ' Set the RecordSource of the subform to the selected table
    Me.MyForm.Form.RecordSource = "SELECT * FROM " & selectedTable ' this is line that triggers error
    ' Refresh the subform to display the data
    Me.MyForm.Form.Requery
End Sub
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Example referencing Form or SubForm fields:
=Forms!FormName!FieldName
Or...
=Forms!ParentForm!SubForm.Form!FieldName

One minor comment, it might be worth naming your Forms in a more descriptive way, and the same with your Controls.
MyFormCommand8 and Text118 might become hard to remember what they do.

Can you confirm that the value from the textbox is what your expect?

Either Debug.Print selectedTable or MsgBox selectedTable.

Yes. It is as it should be.

http://access.mvps.org/access/forms/frm0031.htm

I finally figured it out. When you start the code, i.e. Me.Form.Action
I stopped on the "." and looked through the options listed and finally picked
one that did what I wanted done. So, if the option is not in the list then it
won't work.

Thanks for everybodies help. I appreciate it.