My guess is an argument between the user under which the tvheadend process is running (you if you're using -C, or as specified if you've got -u, or hts as default - ps -eaf | grep tvheadend will tell you) and some elements of your system. The 401 suggests "not authorised" - beyond that, I can't say.
I'd guess at:
Permissions to read/write the configuration files
Permissions to access the webui files
Permissions to access the tuner
... and similar. You may have other error messages around this that give you more information - warnings, for example.