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This page is deprecated as of Eggdrop 1.6.20. You should upgrade instead of applying the fixes below!
./configure your bot.
Open the config.h file in your editor.
Search for (around line 244)
/* Define for Tcl that has threads. */
/* #undef HAVE_TCL_THREADS */
insert the following right after it
#define USE_INTERP_RESULT 1
Carry on with your make config && make && make install.