# Unable to run Screen command

**URL:** <https://psychtoolbox.discourse.group/t/unable-to-run-screen-command/4038>\
**Category:** Programming Help\
**Created:** [September 28, 2021, 10:49pm UTC](https://psychtoolbox.discourse.group/t/unable-to-run-screen-command/4038 "2021-09-28T22:49:05Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![PRwt](https://avatars.discourse-cdn.com/v4/letter/p/bbe5ce/32.png) [@PRwt](https://psychtoolbox.discourse.group/u/PRwt)\
**Post date:** [September 28, 2021, 10:49pm UTC](https://psychtoolbox.discourse.group/t/unable-to-run-screen-command/4038/1 "2021-09-28T22:49:06Z")

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Trying to run on newly install Matlab R2021a with Psychtoolbox-3  
[x,rect] = Screen(0,‘OpenWindow’);  
Error message:

In place of the expected mex file this placeholder file was executed:

Screen

This mex file seems to be missing or inaccessible on your Matlab path or it is dysfunctional:

Screen.mexw64

Hmm. I cannot find the file on your Matlab path?!?

One reason could be that your Matlab path is wrong or not up to date  
for the current Psychtoolbox. You may want to run SetupPsychtoolbox to  
fix possible path problems.

NOTE: You may want to acquire paid priority support for future issues like this.  
Please type ‘PsychPaidSupportAndServices’ to learn more.

Error using AssertMex (line 202)  
Missing or dysfunctional Psychtoolbox Mex file for this operating system. Read the help text above carefully!!

Error in Screen (line 158)  
AssertMex(‘Screen.m’);  
Please advice to solve this problem.

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<div class="post-metadata">

**Author:** ![dcnieho](https://avatars.discourse-cdn.com/v4/letter/d/779978/32.png) [@dcnieho](https://psychtoolbox.discourse.group/u/dcnieho)\
**Post date:** [September 28, 2021, 11:05pm UTC](https://psychtoolbox.discourse.group/t/unable-to-run-screen-command/4038/2 "2021-09-28T23:05:27Z")

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follow all the install instructions, you are probably missing one of the other things you need to install (msvc runtime, gstreamer)