Seems like you've done some custom code modifications and there are some syntax errors

I didn't modify any code. I uploaded an image to the background.

If you know what code to change, please let me know, Ross. I saw a forum with this issue dated 2011 and it didn't provide an answer. Thanks.

Can you switch back to the default theme and try to upload the avatar?

I did. It is still giving me the error, "Please choose image file" when I chose a .jpg file.

I already noted, that there were some changes in the code, here's the third-party javascript code you inserted which breaks avatar uploading:

 </div><script type="text/javascript">$(window).scroll(function() {var final = "input[class='ow_newsfeed_view_more ow_ic_down_arrow']";jQuery( ".ow_newsfeed_view_more_c .ow_button" ).css( "background", "transparent" );jQuery( ".ow_newsfeed_view_more_c .ow_button" ).css( "border", "none" );jQuery( final ).css( "font-size", "0" );jQuery( final ).css( "background", "transparent" );if($(window).scrollTop() + $(window).height() > $(document).height() - && $( final ).is(":visible")) {$( final ).click();$( "#feed1 .ow_newsfeed_view_more_c" ).append('<img src="http://posdit.com/...re/image/loading.gif">' );}if($(window).scrollTop() + $(window).height() < $(document).height() - || $( final ).is(":hidden")) {$( "#feed1 .ow_newsfeed_view_more_c img" ).remove();}});</script><script type="text/javascript">$(document).ready(function(){ BackToTop();
BackToTop({text : '',autoShow :,timeEffect :,effectScroll :'linear',appearMethod :''});});</script><script type="text/javascript">$('a').each(function() {var a = new RegExp('/' + window.location.host + '/'); if(!a.test(this.href) && this.href !='javascript://' ) {$(this).click(function(event) {event.preventDefault();event.stopPropagation();window.open(this.href, '_blank');});}});</script><script type="text/javascript">var lochash = document.location.hash.substr(1);if ( lochash ){var photo_id = lochash.substr(lochash.indexOf("view-photo=")).split("&")[0].split("=")[1];if ( photo_id ){document.location = "http:\/\/posdit.com\/photo\/view\/" + photo_id;}}

you can compare the source code on demo oxwall website and yours and see the difference

I found the page with the beginning of this script. But, the same page does not have "document.location = "http:\/\/posdit.com\/photo\/view\/" + photo_id;" and other parts of the above. I'd like to PM you and give you FTP access for this and my other issue with ads. I uninstalled and reinstalled the Advertisement plugin. The results are still the same.

Remove this third-party javascript code first, then I'll proceed