The bomb was due to an attempt to fix another problem in the database API, had nothing to do with bulk upload of users.
I fixed it a week or so ago, if you grab acs-tcl/tcl/00-database-procs.tcl from the oacs-4-6 branch in CVS you shouldn't see this problem.
Or you can wait until 4.6.2 is tarballed for beta - we're trying to do a code freeze for this version Saturday PM so you shouldn't have to wait long.
