Failed building WebGL Player

I get this message every time try to deploy for WebGL, even in a new clean project.

Any idea how to fix this problem?

Failed running python “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/emcc” @“/Users/Diego/Test_unity/Assets/…/Temp/emcc_arguments.resp”

stdout:
stderr:
Traceback (most recent call last):
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/emscripten.py”, line 1504, in
_main(environ=os.environ)
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/emscripten.py”, line 1492, in _main
temp_files.run_and_clean(lambda: main(
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/tempfiles.py”, line 39, in run_and_clean
return func()
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/emscripten.py”, line 1500, in
DEBUG_CACHE=DEBUG_CACHE,
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/emscripten.py”, line 1384, in main
shared.Building.ensure_struct_info(struct_info)
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/shared.py”, line 1716, in ensure_struct_info
import gen_struct_info
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/gen_struct_info.py”, line 78, in
import sys, os, re, json, argparse, tempfile, subprocess
ImportError: No module named argparse

/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/js-optimizer.js:1844
default: throw ‘whaa?’;
^
whaa?
Traceback (most recent call last):
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/emcc”, line 1452, in
flush_js_optimizer_queue()
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/emcc”, line 1364, in flush_js_optimizer_queue
final = shared.Building.js_optimizer(final, js_optimizer_queue, jcache, debug_level >= 4, js_optimizer_extra_info)
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/shared.py”, line 1592, in js_optimizer
return js_optimizer.run(filename, passes, listify(NODE_JS), jcache, debug, extra_info)
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/js_optimizer.py”, line 375, in run
return temp_files.run_and_clean(lambda: run_on_js(filename, passes, js_engine, jcache, source_map, extra_info))
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/tempfiles.py”, line 39, in run_and_clean
return func()
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/js_optimizer.py”, line 375, in
return temp_files.run_and_clean(lambda: run_on_js(filename, passes, js_engine, jcache, source_map, extra_info))
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/js_optimizer.py”, line 289, in run_on_js
filenames = [run_on_chunk(command) for command in commands]
File “/Applications/Unity/Unity.app/Contents/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/tools/js_optimizer.py”, line 92, in run_on_chunk
assert len(output) > 0 and not output.startswith(‘Assertion failed’), 'Error in js optimizer: ’ + output
AssertionError: Error in js optimizer:

UnityEditor.HostView:OnGUI()

Check this answer. I think it addresses what you were looking at, though I still sometimes get the error. I find removing and putting the build scenes back in helps. http://forum.unity3d.com/threads/failed-building-webgl-player.321433/