If you hurry, then just scroll down until the end of the article to see the solution.

In the last couple of hours I tried to figure this out, because it was really ugly to select some files to upload and then see nothing selected (even if it was selected in the javascript object).
First of all I wanted to make myself sure that everything is configured well, so I’ve opened my previous article about how to use the Magento Flex uploader. Everything was nice, even after the second look. Then it got in my mind that the file uploading shows nicely the selected files before uploading. Compared the code… everything looked good. As a last try I began looking into the flash component’s source code and into the associated javascripts. And the miracle has happened. I simply couldn’t believe it. The reason why it was not working was the undefined maxUploadFileSize javascript variable. Incredible, isn’t it? Lets see the short explanation:

1. after pressing the browse button and when the files are selected, the handleSelect method will be called (we are talking about the Flex.Uploader javascript class which is located in flexuploader.js)

2. handleSelect looks like this:

handleSelect: function (event) {
            this.files = event.getData().files;
            this.checkFileSize();
            this.updateFiles();
            this.getInnerElement('upload').show();
            if (this.onFileSelect) {
                this.onFileSelect();
            }
        },

the problem occurs while trying to call the checkFileSize method.

3. lets see what is there:

checkFileSize: function() {
            newFiles = [];
            hasTooBigFiles = false;
            this.files.each(function(file){
                if (file.size > maxUploadFileSizeInBytes) {
                    hasTooBigFiles = true;
                    this.uploader.removeFile(file.id)
                } else {
                    newFiles.push(file)
                }
            }.bind(this));
            this.files = newFiles;
            if (hasTooBigFiles) {
                alert(
                    this.translate('Maximum allowed file size for upload is')+' '+maxUploadFileSize+".n"+this.translate('Please check your server PHP settings.')
                );
            }
        },

do you see the bolded variables? There are no checks whether the maxUploadFileSizeInBytes or the maxUploadFileSize is defined. When the code execution reaches these checks, it simply breaks the code execution, so handleSelect won’t ever run the remained code.

So for those who just came here and scrolled down for a quick solution:

Define maxUploadFileSizeInBytes and maxUploadFileSize javascript variables in your code, something like this:

    var maxUploadFileSizeInBytes = 2097152;
    var maxUploadFileSize = '2M';

That’s all.