Ok, I tried playing around with this some more. I removed permissions for the plugin from the flickr site. I then deactivated the plugin again. I then reactivated the plugin and tried to reauthorize at Flickr. I get this error when I am done authorizing at the flickr site.
This displays in the flickr tag plugin tab on my blog:
Warning: Cannot modify header information - headers already sent by (output started at /homepages/37/d170032172/htdocs/.../danny/wp-admin/admin-header.php:26) in /homepages/37/d170032172/htdocs/.../danny/wp-content/plugins/flickr-tag/FlickrTagAdmin.php on line 163
Even though it shows this error, the flickr tag plugin tab on my blog shows that I am authenticated to flickr with the correct flickr screen name.
When I refreshed the plugin, that error disappeared. I still do not see the flickr tag option on the write screen.
I hope this helps.