Sounds like i may be having a similar probleem.
Everytime i click the “Add Next Gen Gallery” on the tool bar of posting a page or post it loads the menu window but i get:
500 – Internal Server Error
This is a temporary server error.
Please try to reload the webpage later.
If you are the webmaster of this site please log in to Cpanel and check the Error Logs. You will find the exact reason for this error there.
Common reasons for this error are:
Incorrect file/directory permissions: Above 755. In order files to be processed by the webserver, their permissions have to be equal or below 755. You can update file permissions with a FTP client or through cPanel’s File Manager.
Error im cpanel however says:
[2010-05-25 01:17:48]: error: directory is writable by others: (/wp-content/plugins/nextgen-gallery)
Any Ideas on what may rectify this ??
Regards