I am having the exact same problem. Fresh build with version 3.30 on an Intel Pentium M based system with a brand new HDD. I’m also getting denied access via ftp (only the default admin account is present) and get a file operation error when trying to make a backup. I discovered this after trying to login with winbox today and got a password error. Tried again with no password and got in. Changed the password again and now the Terminal won’t open and returns a login failure. This router has only been up 4 days and already seems to be hosed. Ugh.
Edit: Woops, didn’t realize how old this thread was
My problem ended up being an issue with a license mismatch - a license for a Routerboard was installed on an x86 router. Had to reboot router then paste in a new license.