Some ERPLAB functions, especially filtering functions, use the Matlab 'Signal Processing Toolbox'.
This optional Mathworks toolbox is typically installed with Matlab at the time of Matlab installation.
Sometimes, to save space, this toolboxes are deselected from the Matlab installation. If it is missing, reinstalling Matlab and ensuring the 'Signal Processing Toolbox' checkbox is checked should work.
You can confirm that the Signal Processing Toolbox is installed by running the following command at the Matlab Command Window:
ver
This should show a list of toolboxes installed, like:
