chanstats.tcl by Ernst uses a procedure called [topic] which comes from the days when this command wasn't implemented in eggdrop. Back then Ernst used a different amount of arguments passed to the procedure than is being used by the "regular" command nowadays. Each script, among which CHATstats, making a call to this command will inevitably create the above mentioned error. You have three choices:
1. uninstall CHATstats
2. uninstall chanstats
3. rename chanstats's procedure "topic" and all calls to it to something else.