BlackBerry contacts, calendar, tasks or memos stop syncing. This can be caused by a corrupted BlackBerry Service Book.
We will use the address book for this example, the same action can apply to the contacts, calendar, task or memos.
Go to the address book icon on the BlackBerry and click on the menu, then options. Under Wireless Synchronization change YES to NO and click save. Go back to the address book icon on the BlackBerry and click on the menu, then options. Under Wireless Synchronization change NO back to YES then click save. This action will force the folder to re-sync to Outlook
If this action does not resolve the issue, try the following:
Delete your Service Books and Resend Service Books and remove your battery. It should re-sync.
If this still does not solve the issue try the following. These should be tried independently of each other.
1) Reconcile Now
a. Open the Messages Folder
b. Click the Blackberry Menu button
c. Click Reconcile Now
2) Turn off Wireless Reconciliation and turn it back on
a. On the device go into Messages
b. Click the Blackberry Menu button
c. Select Options
d. Select Email Reconciliation
e. Select Wireless Reconcile, change to "No" r "Off". Click the trackball and choose Save.
f. Then return to the desktop. Repeat the process above and change wireless Reconciliation to "On".
3) Resend the Host Routing Tables
a. Go to Tools > Options
b. Select Advanced Options
c. Click on Host Routing Tables
d. Press the Blackberry button
e. Hit Register Now
f. Look in the Messages to see if it came back that says, “Your handheld has been registered on the wireless network”
g. When this is complete, restart the Blackberry (This will force an update to the host routing table)
4) Hidden option to turn off Wireless synchronization for BES on the handheld and back on
a. Go to Options
b. Select Advanced Options
c. Select Enterprise Activation
d. Type in the email field press and hold the ALT key and type CNFG.
e. Once you enter this a hidden menu will appear and you need to change "Wireless Sync" to No
f. Now exit this menu and wait 30 seconds and repeat the process but turn sync back to Yes.
g. Once you've changed this setting you will see a slow sync will automatically start and it will repair all the wireless sync settings.
Additional Resources: https://wikis.uit.tufts.edu/confluence/display/exchange2010/Troubleshooting+a+Blackberry+that+Stops+Syncing+with+BES