On the BlackBerry device, the following error message appears after pressing the Mute button, accessing an application, or performing a hard reset:
523 app. error. Reset.
Resolution
To resolve this issue, complete the following steps:
1. Upgrade to the latest version of BlackBerry Desktop Software.
+
http://na.blackberry.com/eng/update/
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2. Remove any recently installed applications on the BlackBerry device, then install the latest version of BlackBerry Device Software on the BlackBerry device. For more information about how to upgrade BlackBerry Device Software, see KB03901.
Problem
On the BlackBerry device, the following error message appears after pressing the Mute button, accessing an application, or performing a hard reset:
523 app. error. Reset.
Resolution
To resolve this issue, complete the following steps:
1. Upgrade to the latest version of BlackBerry Desktop Software.
2. Remove any recently installed applications on the BlackBerry device, then install the latest version of BlackBerry Device Software on the BlackBerry device. For more information about how to upgrade BlackBerry Device Software, see KB03901.
From The RIM Knowledge Base
Hope this helps and good luck.