Many clients do not follow the published ActiveSync protocol specification. In fact, even some of Microsoft's products are guilty of this. Horde_ActiveSync attempts to work around those issues that are possible to do so. This page attempts to document some of these idiosyncrasies that we are not (yet?) able to workaround. Some broken behavior seems to be wide spread, and are documented in the General section. More specific behavior is documented in client specific sections.
This status code is issued in response to a SYNC request when the server is unable to locate the folder data in the hierarchy cache. I.e., the folder looks to no longer exist. This can happen when something causes the server stored state to disappear (like when explicitly removing a device from the server) or when something corrupts the stored data. This is supposed to trigger the client to issue a FOLDERSYNC request to freshen the hierarchy cache. Some clients will continue to issue the exact same SYNC request in response to this status code, causing a sync loop. Other clients will accurately issue the FOLDERSYNC request, but fail to update their local cache. Outlook 2013 does this. On receiving new FOLDERSYNC responses, it continues to issue SYNC requests on the old folderids (though it DOES reset the synckey, so something is happening in the client, just not the correct something).
Typically, the only way to resolve this issue is to remove the account from the client and recreate it from scratch.
When moving email items from one folder to another, or deleting them, Outlook does not follow the specification for handling the move, which leads to duplicate email items being present in the destination folder. There are two issues interacting here that cause this. The first, is that Outlook moves the local item on its own, without waiting for the DELETE and ADD commands to be issued from the server. Instead, it reassigns the existing email the new UID received in the MOVEITEMS response. Secondly, when it receives the ADD command for the new email in the destination folder, it fails to treat this command as an UPDATE command as the specification says you must when an ADD command is received for an already existing UID.
If you experience reappearing calendar reminders after you have dismissed them permanently, you can start Outlook with the parameter /cleanreminders to clear the internal list of reminders in Outlook.
Simply press WINDOWS+R and then enter outlook.exe /cleanreminders
If you still get the reappearing reminders you could also set the next reminder to 0 minutes before start in the reminder popup dialog, as that will force Outlook to present the next reminder for that event/appointment right on time. You could also disable all reminders in the Outlook options menu, if you do not need that functionality at all.
Android versions 4.4.0 through 4.4.2 have many issues regarding email synchronization. The largest of which is the inability to download attachments. Attempting to do so normally results in force closing of the Email application. This issue cannot be worked around in code, but is fixed in Android 4.4.3.