First off, this script is buggy. It uses list-commands on untrusted string sources, which is a very, very bad idea. Secondly, the composition of the url used with ::http::geturl does'nt make much sense to me; it's an external string(?) concatenated with a list (from either split:ing $nick or $arg).
split should not be used as an escaping-function; it only servers the purpose of converting a string into a list.
It would also be helpful with some information to which http-package/library you are using. My guess would be that you're using tcl's http-package version 2.x. However, I have not been able to find that error-message in any of the versions I have available.
But to your question, if you don't wish to solve this problem, but just make your bot ignore it, find which command causes the error, and enclose it in a catch-statement (see manpage for catch on how to do this).