>Ok, I did find an active filter on that table that used THISFORM. A coworker suggested, because we can't change the filter expression right now, that I use the table with the AGAIN clause. Does this seem reasonable?

FILTER expression should never use THISFORM in it. You need to set your filter expression though macro, e.g.

lcFilter = "myField = " + thisform.SomeProp

set filter to &lcFilter