PL/TCL functions won't run

Hi all,
    In working through some problems with rows and variables, I
installed PL/TCL into my Postgres 8.0 installation on Windows XP.
Unfortunately, when I try to run any PL/TCL functions, I get the response:

ERROR:  could not create "normal" interpreter

I have ActiveTCL 8.4.9 installed, and createlang succeeded.  Does anyone
have any idea what needs to be done to get PL/TCL to run on my installation?

Thanks,

Eric