(base) C:\Users\MAC Pathak\Documents\Projects\kaggle_stroke_prediction>mlflow ui
Traceback (most recent call last):
  File "c:\programdata\anaconda3\lib\runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "c:\programdata\anaconda3\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\ProgramData\Anaconda3\Scripts\mlflow.exe\__main__.py", line 7, in <module>
  File "C:\Users\MAC Pathak\AppData\Roaming\Python\Python38\site-packages\click\core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "C:\Users\MAC Pathak\AppData\Roaming\Python\Python38\site-packages\click\core.py", line 782, in main
    rv = self.invoke(ctx)
  File "C:\Users\MAC Pathak\AppData\Roaming\Python\Python38\site-packages\click\core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "C:\Users\MAC Pathak\AppData\Roaming\Python\Python38\site-packages\click\core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "C:\Users\MAC Pathak\AppData\Roaming\Python\Python38\site-packages\click\core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "c:\programdata\anaconda3\lib\site-packages\mlflow\cli.py", line 280, in ui
    _run_server(backend_store_uri, default_artifact_root, host, port, None, 1)
  File "c:\programdata\anaconda3\lib\site-packages\mlflow\server\__init__.py", line 138, in _run_server
    exec_cmd(full_command, env=env_map, stream_output=True)
  File "c:\programdata\anaconda3\lib\site-packages\mlflow\utils\process.py", line 34, in exec_cmd
    child = subprocess.Popen(
  File "c:\programdata\anaconda3\lib\subprocess.py", line 854, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "c:\programdata\anaconda3\lib\subprocess.py", line 1307, in _execute_child
    hp, ht, pid, tid = _winapi.CreateProcess(executable, args,
FileNotFoundError: [WinError 2] The system cannot find the file specified
@VikingPathak Seems like a PATH-related issue? Can ensure all the installed binaries are accessible via your $PATH variable on Windows?
@dmatrix  The only path variable that I have provided manually is the mlflow.exe file in the variable name MLFLOW_BIN
          
Add path location of mlflow package to your environment variables if global install check if mlflow is in C:\Users\user\AppData\Roaming\Python\Python37\site-packages.
If you are using Virtualenv use that path such as S:\dir\venv\Lib\site-packages\mlflow.
If problem still persists. Clear pip chache with 'pip cache purge' and redo the above steps.
          
Running into same problem. Tried ak10net's solution, but unfortunately that did not work for me on Windows 10, Python 3.9 and MLflow 1.23.1. Found a similar solution to ak10net's.
Install mlflow in environment:
conda create -n mlflow
conda activate mlflow
pip install mlflow==1.23.0 boto3==1.20.37
Add the directory of mlflow.exe to your path in environment variables:

Don't add this filepath (just a showcase): C:\Users\David\AppData\Roaming\Python\Python38\Scripts\mlflow.exe

Add this dirpath: C:\Users\David\AppData\Roaming\Python\Python38\Scripts
Restart your command prompt / powershell and it should be able to run:

mlflow --version
          
I'm facing the same problem. mlflow works but mlflow ui return the same error.
when I uninstall waitress, mlflow and then reinstall mlflow, it works then. see here.
It seems like there is some version conflict of waitress if you have installed mlflow before. I guess uninstall mlflow will not automatically cleanup waitress.

ps: I got mlflow command not recognized at first.(installed mlflow in a new conda env). After I uninstalled the mlflow from root, then reinstall it in the env, it works.