Sort order by Dlookup field

[1Giggles]

Using Access 2007 in Windows XP:
Is it possible to have a sort order inside my form on a field that looks up something in a table? For instance, I added Text15 that looks up the name associated with the form's particular masterno (which is a text field that is in common with the looked up table). I cannot get the form to sort using [Text15] as OrderBy. Any ideas? I thought it would be simple. Thanks!

[orange]

Please show the Form's recordsource