What can i do for app error 523 - RIM BlackBerry Pearl 8100

Here is the resolution for your problem
Reload the BlackBerry Device Software on the BlackBerry device

Procedure
To use BlackBerry Application Loader to load BlackBerry Device Software, complete the following steps:
1.Install the BlackBerry Device Software on your computer.
2.Open BlackBerry Desktop Manager.
3.Connect the BlackBerry device to the computer.
4.If prompted, type your BlackBerry device password and click OK.
5.Complete one of the following steps:
If the Application Updates Available window appears, click Update Now. The Application Loader Wizard appears.
If the Application Updates Available window does not appear, double-click the Application Loader icon. The Application Loader Wizard appears.
6.Click Next.
7.If prompted, type your BlackBerry device password and click Next. Note: When the Application Loader Wizard is finished examining the configuration on the BlackBerry device, the Device Application Selection screen appears listing the applications available for installation. The selected check boxes indicate applications that are already installed on the BlackBerry device.
8.Select the check box for the BlackBerry Device Software.
9.Click Next.
10.If the On the Device Backup screen appears, choose whether to automatically back up the BlackBerry device and click Next.
11.Click Finish to begin loading the BlackBerry Device Software.
12.Click Close when the software is finished loading.
I hope i was able to help you.