Yup, its the same old problem for me.
As described here.
I can upload the image fine, it shoes up in the uploads folder (checked using FTP), it shows up in the Media Gallery, but as soon as I click insert the window goes white (whith the grey bar and close box along the top) and FF says Done in the bottom left corner.
I am hosted on Media Temple and I first noticed this problem today (19th May 2008). I have tried adding the following code to my root, wp-admin and wordpress directory's .htaccess file and it had no effect.
I have no idea what to do. I re-uploaded all my files as described in the sticky, I re-installed flash, cleared cache and it all made no difference. I don't see this as an upload problem as the file is getting uploaded fine, it's just not getting embedded into the post.