I just installed the Dolphin script last night and while testing I tried to start a new group.  The script allows for starting the group but when I try to post a topic i get this message...
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.

Incorrect Apache directives inside .htaccess file.
Make sure you have not specified unsupported directives inside the local .htaccess file. Such include PHP settings and Apache module settings.
I have gone to th cpanel but cant find any thing wrong.  Any ideas

Charles 

Make sure the directory has permission 755.

Also open folder groups/orca

Rename .htaccess to htaccess.old and try it (just to check).