I think this is the same issue as closed issue #156

INFO: Creating new session
INFO: must not undeclare prefix: line 2, column 0
Traceback (most recent call last):
File "C:\Users\f404632.conda\envs\sp\lib\xml\etree\ElementTree.py", line 1722, in feed
self.parser.Parse(data, False)
xml.parsers.expat.ExpatError: must not undeclare prefix: line 2, column 0

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\src\execution\tabcmd_controller.py", line 43, in run
namespace.func.run_command(namespace)
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\src\commands\auth\login_command.py", line 25, in run_command
session.create_session(args)
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\src\commands\auth\session.py", line 237, in create_session
self._create_new_connection()
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\src\commands\auth\session.py", line 141, in _create_new_connection
self.tableau_server = self._set_connection_options()
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\src\commands\auth\session.py", line 135, in _set_connection_options
tableau_server = TSC.Server(self.server_url, use_server_version=True, http_options=http_options)
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\tableauserverclient\server\server.py", line 97, in init
self.use_server_version()
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\tableauserverclient\server\server.py", line 139, in use_server_version
self.version = self._determine_highest_version()
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\tableauserverclient\server\server.py", line 129, in _determine_highest_version
version = self.server_info.get().rest_api_version
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\tableauserverclient\server\endpoint\endpoint.py", line 186, in wrapper
return func(self, *args, **kwargs)
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\tableauserverclient\server\endpoint\server_info_endpoint.py", line 30, in get
server_info = ServerInfoItem.from_response(server_response.content, self.parent_srv.namespace)
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\tableauserverclient\models\server_info_item.py", line 35, in from_response
parsed_response = fromstring(resp)
File "C:\Users\f404632.conda\envs\sp\lib\site-packages\defusedxml\common.py", line 126, in fromstring
parser.feed(text)
File "C:\Users\f404632.conda\envs\sp\lib\xml\etree\ElementTree.py", line 1724, in feed
self._raiseerror(v)
File "C:\Users\f404632.conda\envs\sp\lib\xml\etree\ElementTree.py", line 1631, in _raiseerror
raise err
xml.etree.ElementTree.ParseError: must not undeclare prefix: line 2, column 0