Recently, when I want to go to blocksadmin page, the following error occur. I didn't change, delete or update anything. All other part of site works well. I use XOOPS 2.2

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Not Acceptable

An appropriate representation of the requested resource /modules/system/admin.php could not be found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
Apache/2.2.9 (Unix) mod_ssl/2.2.9 OpenSSL/0.9.8b mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 PHP/5.2.6 Server
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I think you should contact your hoster about this.
The two cases which reported solved for this problem, were 'some security thingy' and a disk full problem for a temp directory, which then was cleared by the hoster.

Thanks