I copied this text block below since I have the exact same error.
I started with the most recent version, downloaded today.
----
error:
After activating the plug-in I got an error message : "The following directory does not exist - please create it and upload your photos to subdirectories of it:" but there was no directory name/path given. I had read some posts on your site in which you said that the directory should be called 'photos' and be in the wp-content folder so I created the directory .../wordpress/wp-content/photos (chmod to 744) and uploaded a folder (chmod to 777) with some pictures in it to create my first slideshow. When I click on the create simpleviewer slideshow icon in the wp post editing page I still get the same error message, and as before the required directory path is not displaying, in other words what I see is : "The following directory does not exist - please create it and upload your photos to subdirectories of it:" but no directory is written after that!
??
--------------
I have added the paths in the settings link from the admin console. I've tried several variations to the path name in both the image URL dialog box and the path to images dialog box.
I have verified that permissions are set to 777
I'm running WP 2.8
what the heck am I doing wrong? I've looked for proper case, typo's, missing directories, etc. I can't figure this out and it's getting frustrating. I really don't wnat this thing to beat me!