Had similar issue with Plugin Administration giving:
Mahara: Site unavailable A nonrecoverable error occured. This probably means you have encountered a bug in the system
after upgrade to 1.3 RC1 on PHP 5.3.3
Perhaps due to earlier (prior to upgrade) experimentation (installed, then removed) with Learning Styles and Europass CV plugins?
Had similar issue with Plugin Administration giving:
Mahara: Site unavailable
A nonrecoverable error occured. This probably means you have encountered a bug in the system
after upgrade to 1.3 RC1 on PHP 5.3.3
Perhaps due to earlier (prior to upgrade) experimentation (installed, then removed) with Learning Styles and Europass CV plugins?