# MouseMaster Extension "module is not loaded"

**URL:** <https://discourse.slicer.org/t/mousemaster-extension-module-is-not-loaded/48099>\
**Category:** Support\
**Created:** [September 8, 2026, 10:57pm UTC](https://discourse.slicer.org/t/mousemaster-extension-module-is-not-loaded/48099 "2026-09-08T22:57:18Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![jamie.miller.phd](https://avatars.discourse-cdn.com/v4/letter/j/c57346/32.png) [@jamie.miller.phd](https://discourse.slicer.org/u/jamie.miller.phd)\
**Post date:** [September 8, 2026, 10:57pm UTC](https://discourse.slicer.org/t/mousemaster-extension-module-is-not-loaded/48099/1 "2026-09-08T22:57:18Z")

</div>

Problem report for 3D Slicer 5.12.3 win-amd64: Trying to use the MouseMaster extension, but after downloading from extension manager, and installing from file, there is a error message in the module finder “MouseMaster module is not loaded”

Any help with this one would be greatly appreciated.

 ![Screenshot 2026-09-09 105021](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/e/4/e4874d655f147db19565e8555a19245fad62d606.png)

 ![Screenshot 2026-09-09 105033](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/6/c/6cfaa3290611bf26e64117d626712e97f37974fd.png)

 ![Screenshot 2026-09-09 105119](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/e/6/e6f09c24175ed2d551e8eb10a33b1afa4c3e57dd.png)

 ![Screenshot 2026-09-09 105132](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/c/b/cb761727e547ed9c36d3ad8b0957806d8fc718f0.png)

---

<div class="post-metadata">

**Author:** ![jamie.miller.phd](https://avatars.discourse-cdn.com/v4/letter/j/c57346/32.png) [@jamie.miller.phd](https://discourse.slicer.org/u/jamie.miller.phd)\
**Post date:** [September 8, 2026, 10:58pm UTC](https://discourse.slicer.org/t/mousemaster-extension-module-is-not-loaded/48099/2 "2026-09-08T22:58:29Z")

</div>

From Logs; [CRITICAL][Stream] 09.09.2026 10:49:42 [] (unknown:0) - Traceback (most recent call last):

[CRITICAL][Stream] 09.09.2026 10:49:42 [] (unknown:0) - File “”, line 1, in

[CRITICAL][Stream] 09.09.2026 10:49:42 [] (unknown:0) - File “\<frozen importlib.\_bootstrap\_external\>”, line 999, in exec\_module

[CRITICAL][Stream] 09.09.2026 10:49:42 [] (unknown:0) - File “\<frozen importlib.\_bootstrap\>”, line 488, in \_call\_with\_frames\_removed

[CRITICAL][Stream] 09.09.2026 10:49:42 [] (unknown:0) - File “C:/Users/milleja1/AppData/Local/slicer.org/3D Slicer 5.12.3/slicer.org/Extensions-34627/MouseMaster/lib/Slicer-5.12/qt-scripted-modules/MouseMaster.py”, line 14, in

[CRITICAL][Stream] 09.09.2026 10:49:42 [] (unknown:0) - from MouseMasterLib import MouseMasterEventHandler, PresetManager

[CRITICAL][Stream] 09.09.2026 10:49:42 [] (unknown:0) - ModuleNotFoundError: No module named ‘MouseMasterLib’

[CRITICAL][Qt] 09.09.2026 10:49:42 [] (unknown:0) - loadSourceAsModule - Failed to load file “C:/Users/milleja1/AppData/Local/slicer.org/3D Slicer 5.12.3/slicer.org/Extensions-34627/MouseMaster/lib/Slicer-5.12/qt-scripted-modules/MouseMaster.py” as module “MouseMaster” !

[CRITICAL][Qt] 09.09.2026 10:49:42 [] (unknown:0) - Fail to instantiate module “MouseMaster”

---

<div class="post-metadata">

**Author:** ![jamesobutler](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jamesobutler/32/7511_2.png) [@jamesobutler](https://discourse.slicer.org/u/jamesobutler)\
**Post date:** [September 9, 2026, 12:48am UTC](https://discourse.slicer.org/t/mousemaster-extension-module-is-not-loaded/48099/3 "2026-09-09T00:48:39Z")

</div>

@benzwick It looks like you forgot to include in the CMake infrastructure the MouseMasterLib of files.

[https://github.com/benzwick/SlicerMouseMaster/blob/9bebc08d1339f1bfeb90b7168c203a8d8f408e19/MouseMaster/CMakeLists.txt#L2-L11](https://github.com/benzwick/SlicerMouseMaster/blob/9bebc08d1339f1bfeb90b7168c203a8d8f408e19/MouseMaster/CMakeLists.txt#L2-L11)

---

<div class="post-metadata">

**Author:** ![benzwick](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/benzwick/32/80521_2.png) [@benzwick](https://discourse.slicer.org/u/benzwick)\
**Post date:** [September 9, 2026, 2:10am UTC](https://discourse.slicer.org/t/mousemaster-extension-module-is-not-loaded/48099/4 "2026-09-09T02:10:53Z")

</div>

Thanks @jamie.miller.phd and @jamesobutler - I will try to fix this.