I’m having the same problem. I can see the following in my apache logs:
196.215.19.226 - - [29/Apr/2011:07:29:02 -0400] "GET /blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker HTTP/1.1" 200 7523 "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
196.215.19.226 - - [29/Apr/2011:07:29:06 -0400] "GET /blog/wp-content/plugins/akismet/akismet.css?ver=3.1.2 HTTP/1.1" 304 - "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
196.215.19.226 - - [29/Apr/2011:07:29:06 -0400] "GET /blog/wp-includes/js/imgareaselect/imgareaselect.css?ver=0.9.1 HTTP/1.1" 304 - "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
196.215.19.226 - - [29/Apr/2011:07:29:06 -0400] "GET /blog/wp-admin/css/colors-fresh.css?ver=20110121 HTTP/1.1" 304 - "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
196.215.19.226 - - [29/Apr/2011:07:29:06 -0400] "GET /blog/wp-includes/js/l10n.js?ver=20101110 HTTP/1.1" 304 - "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
196.215.19.226 - - [29/Apr/2011:07:29:06 -0400] "GET /blog/wp-content/plugins/akismet/akismet.js?ver=3.1.2 HTTP/1.1" 304 - "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
196.215.19.226 - - [29/Apr/2011:07:29:06 -0400] "GET /wp-content/plugins/gallery3-picker/gallery.js?ver=3.1.2 HTTP/1.1" 404 13460 "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
196.215.19.226 - - [29/Apr/2011:07:29:07 -0400] "GET /wp-content/plugins/gallery3-picker/jquery.jstree.min.js?ver=3.1.2 HTTP/1.1" 404 13470 "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
196.215.19.226 - - [29/Apr/2011:07:29:09 -0400] "GET /wp-content/plugins/gallery3-picker/gallery.js?ver=3.1.2 HTTP/1.1" 404 13454 "https://www.highpeak.co.za/blog/wp-admin/media-upload.php?post_id=241&type=image&tab=gallery3_picker" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
Looks like I’m getting some 404 errors but I don’t know why. Cany anyone shed any light please?
Gallery 3.0.1
WordPress 3.1.2
I’ve tried with and without guest REST access.