# Fatal Python error: Py\_Initialize: unable to load the file system codec

**URL:** <https://discourse.slicer.org/t/fatal-python-error-py-initialize-unable-to-load-the-file-system-codec/14115>\
**Category:** Development\
**Created:** [October 18, 2020, 3:05pm UTC](https://discourse.slicer.org/t/fatal-python-error-py-initialize-unable-to-load-the-file-system-codec/14115 "2020-10-18T15:05:15Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Warthou](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/warthou/32/9023_2.png) [@Warthou](https://discourse.slicer.org/u/Warthou)\
**Post date:** [October 18, 2020, 3:05pm UTC](https://discourse.slicer.org/t/fatal-python-error-py-initialize-unable-to-load-the-file-system-codec/14115/1 "2020-10-18T15:05:16Z")

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Hello everyone,

I have downloaded and built 3DSlicer. However, I am now running into these runtime errors:

[SSL] Failed to load Slicer.crt  
Fatal Python error: Py\_Initialize: unable to load the file system codec

Visual Studio tells me it’s occurring from this line:

PythonQt::init(flags);

So I thought I needed to download PythonQt but it did not help. Does anyone know why these errors could be happening?

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**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [October 18, 2020, 3:09pm UTC](https://discourse.slicer.org/t/fatal-python-error-py-initialize-unable-to-load-the-file-system-codec/14115/2 "2020-10-18T15:09:10Z")

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Most likely you have some other Python in your path and/or you did not start Visual Studio with `Slicer.exe --VisualStudio`.