Without. Our htaccess strips out www.
Then make sure you or your client DON'T login using www.site.com/manager/ that will break the path and show a blank interface.
If this is not the case try different browsers and computers AND compare the URL of the window that works and that of which isn't.
Hey there mrhaw- thanks for the suggestions. I did see the previous post you had linked to and I looked into it prior to this post. I inspected my htaccess, etc. but this happens regardless of www being present when logging into the manager. Our htaccess strips www entirely. Thanks again.
If I click on the open browser button in insert/edit link popup a KCFinder window opens with the url manager/media/browser/mcpuk/browse.php?opener=tinymce&type=files
This KCFinder window searches the files in assets/files here. Is the folder assets/files available and writable in your installation?
Is that window white or gray (could you get the response header i.e. with firebug)?
Are there any files with umlauts in the folder?
Ahhhhh..... figured it out:
Jako, your question about files with umlauts prompted me to take a closer look at the contents of the files directory. It turns out someone created a symlink to (drumroll) files->files! So it was caught in an endless loop. I deleted the dreaded infinite-looping symlink and all is well.
Thanks Jako & mrhaw for your help. Case closed.