Additional error
fyi, In the case where the library.php file is called prior to the CachedResize_Image.php file this is the error occurring:
Warning: imagejpeg() [function.imagejpeg]: Unable to open '../image_cache /images/100/proportion/image_09_w75_h50/image_09_01161024.jpg' for writing: Invalid argument in \webassist\caching\CachedResize_Image.php on line 207