There is more than one installation using dotlrn 2.2 upgraded and so far no one else has reported this error.
The way ad_form works, entirely in Tcl, it does not seem that it should be affected by an upgrade, which mainly would should a probem in the database code.
I can't test on FC4 but I'll try a new install of dotlrn 2.2 from the tarball and see what I find.