Well, that is a bit odd.
My suggestion. Remove the str shortcode option from the shortcode and reactivate the template. I suppose somehow one of the translated strings is causes this. So removing them and adding them one at a time will allow you to identify exactly which string. After you isolate the string let me know which one and what the exact string you are using. I need this so I can duplicate the error.
Hope that helps! Let me know what you find.
ps. I recommend starting with the str_image option since that is being used on the line of code the error is reporting.