Forum OpenACS Q&A: Re: Invalid command name "::thread::create", invoked from within ns_mutex eval ns_mutex::throttle
throttler is a special thread which is created at load time by xotcl-request-monitor. For this to happen, thread support should be there at that specific point in time (e.g. loading of xotcl-request-monitor tcl files at startup).
I would suggest against hacking the Thread library in this or that file. Instead, please try to find the root cause of your issue: most likely and for reasons still unknown, Naviserver is not finding the thread library at startup.
As suggested before, the config file of your instance and the log file should give you the elements to find out what is going on.