WP Image Upload Issue

This is an urgent issue.
When uploading images via media uploader, the images sometimes won’t upload!! The progress bar shows on the image but does not progress further.

Cleaning Cookies and Cache sometimes resolved the issue, but not always. The file sizes are around 70KB. I can upload files easily via FTP. I often have to log out of wp and log in again, and this often solves the issue, but not always!

I have this issue on two wp sites that I administer, and the issue is interfering with productivity. I have tried everything I can think of but no luck!

I need this solved, if someone has an answer. This is an urgent issue.

Thanks