1) Make sure you have Blackberry Desktop Manager installed.
2) On your PC, go to Start > Run and copy and paste the following line exactly (meaning with the quotation marks):
"c:\program files\common files\research in motion\apploader\loader.exe" /nojvm
3) The Application Loader Wizard will appear -- click "Next."
4) In the "Connection:" drop-down menu, you should see "USB-PIN: UNKNOWN". Click the "Next" button.
5) You should then see a list of applications ready to be installed for your Blackberry. Hit Next and Finish and you are well on your way to getting your Blackberry back to life. Congrats! Just don't disconnect anything and let the lengthy process finish completely.
NOTE: If you do not see a list of applications mentioned in step 5 and instead see the message "The Blackberry Desktop Software does not have Blackberry Device Software for the device that you have connected to the computer. Contact your wireless service provider or system administrator," then you must download Blackberry's Operating System for your carrier and device.
Just select the appropriate carrier and network type, select your Blackberry model from the list and download the latest version. Install this download and follow the above steps again and you should be on the right path.
"Error 523", "App Error 523", or "JVM 523" appears on the BlackBerry smartphone
Article ID: http://www.blackberry.com/btsc/KB10144
KB10144 How to force the detection of the BlackBerry smartphone using Application Loader
I got that from: http://supportforums.blackberry.com/t5/BlackBerry-Curve/App-error-523-reset/td-p/1743575