I have been having this same problem, and nothing suggested so far has fixed it, but here is the seriously odd thing. My Boyfriend uses my computer and when HE signs in on ijournal there is no problem, but whenever I try to post, either to my own journal or a community, I get the "server error" message. Weird. I have my full birthdate up and a valid email and all...

it has been suggested that you should try deleting your Library/Preferences/com.warped.iJournal.plist

and see if you can then login.

Yeah. that happened to me...it keeps saying "This is Read-Only" and it won't work.