Why do I get an "Error in sl_customization" when I start Simulink?

While trying to start Simulink, or when I open any Simulink example, I see a warning in the MATLAB Command Window that contains an "Error in sl_customization". 

Warning: Unrecognized function or variable 'slReloadToolstripConfig'.

Error in sl_customization (line 3)
    slReloadToolstripConfig;
 
> In slCustomizer/callAll
In slCustomizer/refresh
In slCustomizer.staticRefresh
In simulinkrc (line 51)
In Simulink.start_simulink 

Why do I get this warning, and how can I avoid it?

Answer 1

[MathWorks Support Team]

When Simulink is started, the command "sl_refresh_customizations" is executed. As a result, all "sl_customization.m" files on the MATLAB path and in the current folder are run. The message "Error in sl_customization" indicates one of these "sl_customization.m" files contain faulty code and could therefore not be executed.

Run the following command in the MATLAB Command Window to get a list of  all "sl_customization.m" files on your MATLAB path:

>> which -all sl_customization

Then, go through the listed "sl_customization.m" files and inspect their source code. In the particular example presented in this article, the warning was caused by an "sl_customization.m" file that had a call to "slReloadToolstripConfig" in line 3. This function was only introduced in R2021b and will lead to an "unrecognized function" error when executed in R2021a and prior.

Note that "sl_customization.m" files are often on your MATLAB path as part of a third-party toolbox or blockset. Sometimes, toolbox authors choose to obfuscate the "sl_customization.m" file, so that only an "sl_customization.p" is present which cannot be opened. If the warning only occurs when this "sl_customization.p" file is present on the path, reach out to the toolbox author to fix the source code.