I believe I have resolved the "Cannot connect to pocket" error using Palm Treo 750V, this should also work on other devices.
I am running windows mobile 6 and used the following two programs
SDA Application Unlock
http://www.gpcarreon.com/SDA_ApplicationUnlock.zip
PHM RegEdit
http://www.freewareppc.com/utilities/phmregistryeditor.shtml
**If you have previously used SDA application unlock on the Treo 750v you may have noticed it initially says "This device cannot be unlocked" and then immediately after says "This device has been unlocked, please reboot the SDA" ...this is an error and the device was not successfully unlocked!!
How to resolve
1)Install PHM RegEdit and open it and look for "HKEY_LOCAL_MACHINE" and expand it to
HKLM\Security\Policies\Policies
This is also explained here http://www.mvdirona.com/jrh/SmartPhone/AppAndSimUnulock.htm
2) My values on the Treo750v(Vodaphone) were initially
00001000 = 2
00001005 = 16
I changed them as the page above mentioned
Value 1001 should be set to 1
Value 1005 should be set to 40
3) Save both changes
4)Reset the Treo 750v
5) Delete the Syncmate driver from Device/Windows/AppMgr/ELTIMA Syncmate/Driver
6) Uninstalled Syncmate from my Mac running Leopard and rebooted the machine
7) Reinstalled Syncmate and rebooted the machine.

After reboot connect the phone with USB cable, it will prompt for driver installation of "Smartphone2005arm.cab" on your Windows Mobile...install the driver and reset phone
9) After installation press "Connect Now", it should find your device and then you should see the "Sync Now" button in Syncmate..if you don't then reset your phone one more time, it should work after this!
10) Please post if this works on other devices that have the "cannot connect to pocket" error
**Eltima, I have been installing betas since the very first one and resolved this problem for the Treo750 v and hope you will be gracious enough to provide a free license..Syncmate may have worked for the Treo750(North America) but it will not work with the Treo 750V which is the Vodaphone version.
**Simply running SDA application unlock as Eltima has suggested WILL NOT work, it may tell you the device has been unlocked but it truly has not been...you MUST make the registry edits as explained above to solve the "pocket cannot connect" error
I hope this information will help others resolve the cannot connect error, I take no responsibility for edits you make to your registry..make note of any changes you may make in case you need to return your phone to its original condition..here is my log as proof it works now.
=====================================================================
BackService version: 0.4.1d6
USB driver version: 0.2.3b2
Device platform PocketPC
Device CpuType 2577
Device Version 81199621
Device OS Version 5.2
Device ModelName Palm Treo 750
Installing driver on pocket...
Cant connect to Pocket
Driver found. Starting...
Cant connect to Pocket
Device platform PocketPC
Device CpuType 2577
Device Version 81199621
Device OS Version 5.2
Device ModelName Palm Treo 750
Driver found. Starting...
Pocket driver version: 1, 0, 0, 277
BEGIN SYNCING...
Event 'syncRefresh' for plugin: Contacts
Event 'syncRefresh' for plugin: iCal
Beginning a sync session...
NEGOTIATING entities to push to the sync engine...
Slow syncing entityName=com.apple.contacts.Contact...
Event 'syncServicePush' with entity: com.apple.contacts.Contact for plugin: Contacts
Contacts in history - 0
Add 268 contacts from Pocket
Change 0 contacts from Pocket
Del 0 contacts from Pocket
Slow syncing entityName=com.apple.contacts.Group...
Event 'syncServicePush' with entity: com.apple.contacts.Group for plugin: Contacts
Slow syncing entityName=com.apple.contacts.Phone Number...
Event 'syncServicePush' with entity: com.apple.contacts.Phone Number for plugin: Contacts
Slow syncing entityName=com.apple.contacts.Email Address...
Event 'syncServicePush' with entity: com.apple.contacts.Email Address for plugin: Contacts
Slow syncing entityName=com.apple.contacts.Street Address...
Event 'syncServicePush' with entity: com.apple.contacts.Street Address for plugin: Contacts
Slow syncing entityName=com.apple.contacts.Date...
Event 'syncServicePush' with entity: com.apple.contacts.Date for plugin: Contacts
Slow syncing entityName=com.apple.contacts.Related Name...
Event 'syncServicePush' with entity: com.apple.contacts.Related Name for plugin: Contacts
Slow syncing entityName=com.apple.contacts.URL...
Event 'syncServicePush' with entity: com.apple.contacts.URL for plugin: Contacts
Slow syncing entityName=com.apple.contacts.IM...
Event 'syncServicePush' with entity: com.apple.contacts.IM for plugin: Contacts
Slow syncing entityName=com.apple.calendars.Calendar...
Event 'syncServicePush' with entity: com.apple.calendars.Calendar for plugin: iCal
Slow syncing entityName=com.apple.calendars.Event...
Event 'syncServicePush' with entity: com.apple.calendars.Event for plugin: iCal
Events in history - 0
Add 21 events from Pocket
Change 0 events from Pocket
Del 0 events from Pocket
Slow syncing entityName=com.apple.calendars.Recurrence...
Event 'syncServicePush' with entity: com.apple.calendars.Recurrence for plugin: iCal
Slow syncing entityName=com.apple.calendars.DisplayAlarm...
Event 'syncServicePush' with entity: com.apple.calendars.DisplayAlarm for plugin: iCal
PUSHING changes to sync engine for entities (
)
MINGLING, invoking prepareToPullChangesForEntityNames: with filteredEntityNames=(null)
PULLING changes from the sync engine...
Event 'syncServicePull' for plugin: Contacts
Found same on mac - 0
Add 0 contacts from MAC
Change 0 contacts from MAC
Del 0 contacts from MAC
Event 'syncServicePull' for plugin: iCal
Found same events on mac - 0
Add 381 events from MAC
Change 20 events from MAC
Del 0 events from MAC
Committing accepted changes...
Ended sync session.
Event 'sync' for plugin: Contacts
Event 'sync' for plugin: iCal
Event 'syncCommit' for plugin: Contacts
Event 'syncCommit' for plugin: iCal
END SYNCING