What version of RadiusNT are you using?  I'm using 2.5.213 and recently
noticed the same problem.  I don't remember it happening with older versions
though.  I'm using SQL Server 7 SP2 and MDAC 2.5 is installed on all
machines.
Josh
For more information about this list (including removal) go to:
http://www.iea-software.com/support/maillists/liststart