Magento 1.4.2 not displaying/saving product images on frontend & backend

My Magento 1.4.2 site suddenly developed the following problem:

When uploading product images, the images appear to have successfully uploaded & are visible when I rollover the image but as soon as I save the image 'disappears' and is not saved to the media subfolder. Hence it is not displayed. The permissions on the folders are set to writeable. I have cleared the cache; re-indexed stock-status, product flat data...; renamed media/.htaccess; renamed php.ini.sample to php.ini & changed memory_limit from 64M to 512M.

The prob开发者_Python百科lem persists. Any ideas? Thanks

---

Is it possible that you've updated Prototype to version 1.7? If so, you'll have to change foo.toJSON() calls in js/mage/adminhtml/product.js to Object.toJSON(foo).