Getting bizarre error

Getting this error when attempting to change archive display settings

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Forbidden
You don't have permission to access /_admin/book.archive.php on this server.
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Will this have anything to do with updating to 1.2 from 1.0? Do I need to do a clean install of Grawlix instead? I also had a similar issue when trying to create a new page:

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Forbidden
You don't have permission to access /_admin/book.page-create.php on this server.
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Hopefully you can help me out here!

Thanks