I was using WordPress 3.1.3. I also used WordPress 3.1.0, 3.1.1 and 3.1.2, but all with them, I got the image uploading problem. But in wordpress 3.0.4 (now I am using this version) is out of that problem. And now I will tell you that how to back into wordpress 3.0 version or later. But one thing, remember, it is not easy if you have not enough idea about that as it will destroy your hole site if you miss.
Well, I did this trough my cPanel (Hosting control panel). If you have hosting control panel, open it and go to the file manager and open the root of your wordpress directory. First, we will take a backup for the necessary files to skip any risk. Well, make a folder named “Backup” or anything you like. Now copy the file named “wp-config.php” (Select and see the top menu of the window to get the Copy option. You may als0 get this option by right click upon that file. Choose the directory for copy on the upcoming dialog box) into the backup folder. wp-config.php contains the database name, site host, username and password and more information of your hosting to connect with the database and run your site. Now back to the root folder and select the wp-content to make a zip copy of that folder(See the upper menu and choose Compress). wp-content contains all the themes, plugins and media files uploaded through WordPress. Now make a backup of the wp-content.zip (or what folder extension you chooses for to compress the wp-content folder)
NB. If you like, you may also take a backup of your database used on your site. Go to phpmyadmin from the cpanel to take a database backup, see the post here.
Now, Upload the old version of wordpress. It may be wordpress 3.0.0 or later, (I have added the wordpress-3.0.4 on mediafire. You may download it from here. or Download it from WordPress Archive ) I uploaded wordpress 3.0.4 (wordpress-3.0.4.zip) . Actually we are going to update the wordpress engine on the hosting. To upload it you may use uploader of your cpanel or you may use any ftp application. I use my cpanel uploader to upload the old version. Well, now extract the zip file (file name look like wordpress-3.0.4.zip or anything if you rename it before). It will create a wordpress folder on the same directory where you uploaded the wordpress zip file. Now open the wordpress folder on the directory and select all the files and folders except the wp-content folder. Now choose copy or move from the menu (you may also get those option by right click on the selected files) and copy or move the all files and folders into the root folder. Now call the wp-admin through your browser (http://yoursite.com/wp-admin) and follow the instruction. Hope you will successfully do it and your wordpress will back to the old version. One thing again! It may harmful if you don’t have enough idea about that as it may cause to brack your site! Hopefully you do not need to replace the wp-content folder and wp-config.php file. But we did a backup to avoid any risk. Enjoy, If everything is OK delete the backup files. I will right back with more about that.