When you set the plugin parameter "Process all images", then the plugin starts to process all images in a site content, which is processed by content plugins includes content of some modules, such as "Custom html" module. You can find the parameter "Prepare content" on tab "Options" for such modules.
In your case the problem is for the content of the component com_attachments. There may be many reasons for error: images are packing with a way, which is not supported by GD2 library of your server (system function "getimagesize"); plugin SmartResizer has the limits for image names - no uppercase, no special symbols, no national symbols. Lastly (I think in your case) the path for image is not complete for some reasons: your path is "/media/com_attachments/images/file_icons/link_arrow.png", but should be "[rootsitefolder]/media/com_attachments/images/file_icons/link_arrow.png" or "
yoursite.com/media/com_attachments/image...icons/link_arrow.png" or at least "media/com_attachments/images/file_icons/link_arrow.png" (without starting a slash). What is the reason of the incorrect path - I do not know. It is individual for each case. This requires careful analysis and a long testing at various sites, platforms and under different conditions. I will fix known issues of the plugin Smartresizer, when I have a time for this free extension. Unfortunately now all of my time engaged in the development of commercial components.
Now I advice you to turn off the plugin parameter "Process all images" and use "smartresize" class for images you need to process (see the plugin documentation). Also you can turn off warnings and notices in Joomla basic parameters to switch off such warning messages.