Problem: Remember the Milk cannot sync on Windows Mobile

Problem: Remember the Milk cannot sync on Windows Mobile

Solution:
Unfortunately there is no solution (yet) to this problem. Keep checking back because I'll be posting the solution here immediately after I have resolved this annoying problem.

On my device I installed MilkSync, the portable application from Remember The Milk's GTD website. It is version 1.0.0 dated 2007.
My device: HTC HD2, Windows Mobile 6.5

MilkSync produces a few error messages in a few different scenarios: 

• Syncing through ActiveSync / USB-to-PC / WiFi

- Status message 'Connecting...' is displayed for about 30 seconds
- After that this error message pops up: "Error: Cannot establish an Internet connection."
- _any_ other application can connect to the internet (http or https protocol)
- I don't use a proxy server

• Syncing through mobile internet / 3GSyncing through mobile internet / 3G

- Status message: 'Connecting...' -> Sending tasks 1-... -> Waiting for server data ... -> Finished receiving -> Ending
- After that - or sooner!! - this error message pops up: "Authentication failed. Check username and password of Pro account status."
- The odd part is, that some tasks _do_ get synchronized, despite the 'authentication failed' error message.
- After uninstalling the MilkSync app and subsequent installation, the server requests a re-sync. When there are less than about 75 tasks on the mobile device, the synchronization process is completed without error messages. ...most of the times

Until now RTM hasn't come up with a solution to the problem...