23rd February, 2012
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EllisLab are currently undergoing maintenance. As a result, their website is returning a “401 Unauthorized” page to anyone who visits it.
The handy “ExpressionEngine Info” accessory (which is built into ExpressionEngine and enabled by default) reports on the latest version available for download. Unfortunately, this accessory doesn’t check whether its request was successful before it tries to parse it and determine the latest EE version.
Put these two together, and you have a nasty PHP error displayed every time a user tries to access your Control Panel. This could also happen any other time the ExpressionEngine Info accessory fails to connect to expressionengine.com to check for updates (e.g. a server firewall blocking your connection, or a temporary outage).
A quick fix is to simply uninstall the ExpressionEngine Info accessory under Add-Ons > Accessories. You can also find the system/expressionengine/accessories/acc.expressionengine_info.php file and rename it to something else (say, disabled.acc.expressionengine_info.php). This will temporarily disable the accessory, and allow you access to your control panel.
If you seeing this error, but are sure that expressionengine.com is available from your web server, you should be able to fix the error simply by deleting the system/expressionengine/cache/ee_version directory from your server (it will be recreated next time the accessory checks for updates).
Hopefully in future this accessory can be updated to check for a successful response before trying to parse the latest version of EE from EllisLab’s website.