WebGL Build Errors - Forces computer restart to make it work

Unity Engine
1

Building webGL works fine once, but after the first build, if I try to build again. I get this error. It only goes away and builds successfully if I restart my computer. Any ideas?

Failed running "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport/BuildTools/Emscripten_Win/python/2.7.5.3_64bit/python.exe" "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport/BuildTools/Emscripten/emcc" @"D:/Crystal Fountains/Crystal/WaterLab Unity/WaterLab/Assets/../Temp/emcc_arguments.resp"

stdout:
stderr:
warning: unresolved symbol: glProgramParameteri
warning: unresolved symbol: glFlushMappedBufferRange
warning: unresolved symbol: glGetInternalformativ
warning: unresolved symbol: pthread_create
warning: unresolved symbol: _ZN4FMOD13DSPConnection6setMixEf
warning: unresolved symbol: glUnmapBuffer
warning: unresolved symbol: glGetStringi
warning: unresolved symbol: glProgramBinary
warning: unresolved symbol: glMapBufferRange
warning: unresolved symbol: glGetProgramBinary
warning: unresolved symbol: glCopyBufferSubData
Traceback (most recent call last):
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport/BuildTools/Emscripten/emcc", line 1540, in <module>
    flush_js_optimizer_queue()
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport/BuildTools/Emscripten/emcc", line 1447, in flush_js_optimizer_queue
    run_passes(chunks[0], title, just_split=False, just_concat=False)
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport/BuildTools/Emscripten/emcc", line 1420, in run_passes
    final = shared.Building.js_optimizer(final, passes, debug_level >= 4, js_optimizer_extra_info, just_split=just_split, just_concat=just_concat)
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\tools\shared.py", line 1578, in js_optimizer
    ret = js_optimizer.run(filename, passes, NODE_JS, debug, extra_info, just_split, just_concat)
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\tools\js_optimizer.py", line 520, in run
    return temp_files.run_and_clean(lambda: run_on_js(filename, passes, js_engine, source_map, extra_info, just_split, just_concat))
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\tools\tempfiles.py", line 39, in run_and_clean
    return func()
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\tools\js_optimizer.py", line 520, in <lambda>
    return temp_files.run_and_clean(lambda: run_on_js(filename, passes, js_engine, source_map, extra_info, just_split, just_concat))
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\tools\js_optimizer.py", line 435, in run_on_js
    filenames = pool.map(run_on_chunk, commands, chunksize=1)
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten_Win\python\2.7.5.3_64bit\lib\multiprocessing\pool.py", line 250, in map
    return self.map_async(func, iterable, chunksize).get()
  File "C:\Program Files\Unity 5 f4\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten_Win\python\2.7.5.3_64bit\lib\multiprocessing\pool.py", line 554, in get
    raise self._value
AssertionError: Error in optimizer:

UnityEditor.HostView:OnGUI()
2

Could you please try to reproduce it 5.3.3 ? If that does not solve the problem, then I would suggest you submit a bug report with a simple project so we can investigate.