Uploading pictures

After we updated to the new version of WP we got a lot of problems with uploading pictures. Usualy it says that WP could not load up to wp-conten/uploads/2011/01.
When I look with my FTP I see that WP has loaded upp pictures with 0kb. I have to delete these manualy and try to use FP again. Sometimes it works sometimes not. We are two with the same problems.