Hey Jose,
On line 790 we are tryign to create your images folder. Unfortunately we don't use JFolder::create here, but plain old mkdir. (which I've changed now to jfolder::create). Because we use mkdir we can't create nested categories. So if in the settings of matukio you've entered a nested image path and it's not existing in the images folder, then that's why you get the warning.
I've pushed my changed to the matukio branch, but Yves won't be here till Monday, so you can expect a new version first then.
Regards,
Daniel
P.S. You can always suppress those warning and you should suppress them on production sites. Go to your global config and set error reporting to none.
