Some possible reasons for this (or similar) errors:
1. Forgetting to include the TypoScript static templates
This will activate the TypoScript under Configuration/TypoScript

2. Wrong path
The Template paths set via TypoScript must match the available template paths in the filesystem.
Usually, the default path is:
- Resources/Private/Templates (for frontend plugins)
or
- Resources/Private/Backend/Templates (for backend modules)
This must have been set correctly via TypoScript. For example:
Configuration/TypoScript/setup.typoscript:
module.tx_myexample_web_myexamplelist {
view {
templateRootPaths.0 = EXT:myexample/Resources/Private/Backend/Templates/
...
- module. is for backend modules
- if you are working with frontend plugins, use plugin. instead of module.
- the correct file ending for TypoScript is .typoscript since TYPO3 8 and no longer .ts or .txt. For version 7, it is correct to use .ts.
3. Incorrect filenames
Make sure that the name of the Controller matches the name of the subdirectory in the Templates directory. The name of the template file is capitalized.
- Controller/SomeController.php: listAction()
matches
- Resources/Private/Backend/Templates/Some/List.html
Where to define the TS:
- either as described above e.g. in Configuration/TypoScript setup.typoscript (and load this via static include).
- The file ext_typoscript_setup.typoscript in the extension root can be used to setup TypoScript independent of page-tree and template-records. This will be included in the setup section of all TypoScript templates. but also consider the warning in the documentation.
- Load TypoScript or TypoScript files directly in the extension with functions from ExtensionManagementUtility