You must be trying to directly open a .mex from an RTD example folder
(<Your_RTD_Install_Dir>\eclipse\plugins\<Drv_Name>\examples\S32DS\<Example_Name>\)
It is not a valid way to work with this package.
To do it properly, you have to install RTD as an update/extension to S32DS:

then create a new project by following "File->New->Project from Example" menu path and
select the desired example:

When you follow this way, S32DS copies the example to your workspace and prepares it for
making modifications.
Hope this helps,
Platon