Hello,
You may have the 3.4.0 free version installed, with the Pro module iC Event List...
Due to many code improvement in 3.4.0, as well as for the component (with new library) and module, this could be the reason for your module returning error, as the thumbnails generator has moved, and been improved.
What you can do first is to disable the thumbnails generator in global option (it should solve the error message).
Then, you will have to edit the module to be able to use the new iC library and iCagenda Utilisies functions.
I will see next week how to handle this with code changes, to allow you to use the module iC Event List with a free version.
And then, will give you the code to be changed to able thumbnails generation
Keep in touch!
Best Regards,
Cyril