If you run Eudora 7 like I do, and windows 7 or later, you may get this error:
"eudora was unable to update the system registry"
here is how I fixed it.
Eudora is trying to see what the default email client is, and may want to change it, even if you tell eudora not to check, it still checks. Windows 7 has severe protection on the registry.
If you cannot, you will have to take ownership or give yourself or everyone full control of the shell key and several sub keys.
you may have to hit f5 or try to create a sub key to get the open and command keys to appear. do not change anything. open eudora and it should no longer give the annoying message. If this does not work do not contact me for further help, it works for me.