I posted this on Sunday in the "general" section and didn't get a reply, so I think I should have instead posted this in the "pluploadqueue" forum, as it appears to be a pluploadQUEUE problem:
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When using PlUpload 2.1.1. (latest stable release) and when uploading several medium-sized files (~150 MB) using the "plUploadQueue" with a TomCat Java back-end, it *will* work if the network is not congested; however, if we simulate network congestion (by downloading/uploading large files from other computers), then the plUploadQueue will start fine, but somehwere in the middle of the upload, the plUploadQueue js widget will just return "http error". There are no discernible errors on the server side (Tomcat). Any thoughts/fixes/suggestions? Is there a way of getting the plUploadQueue to report more descriptive error messages?
My plUploadQueue settings are indicated below. (Note: The "plUploadQueue" js code is actually called via GWT, but I'm 99.5% sure that is not relevant.)
... 
    $wnd.$("#" + divID).pluploadQueue({
        // General settings
        runtimes : 'html5',
        url : url2,
        max_file_size : '40000mb',
        chunk_size : '128kb',
        unique_names : false,
        multiple_queues : true,
        headers : {
        'targetFolder' : targetFolder2,
        'uploadJobString' : uploadJobString2,
    },
         //Resize images on clientside if we can
        resize : {width : 320, height : 240, quality : 100},
   
        // Flash settings
        flash_swf_url : 'builtinds/sc/plupload/js/plupload.flash.swf',
        // Silverlight settings
        silverlight_xap_url : 'builtinds/sc/plupload/js/plupload.silverlight.xap'
    });
    }
...
My theory is that (somehow) the front-end plUploadQueue js got "confused" and failed to transmit a packet and it doesn't retry?