CPUU shows the following error while logging on to the source Outlook profile:
[Trace] Open store '[mailbox]@[mail_domain].com'.
In the beginning of the CPUU log file, right before the INI file settings are listed, you can see the following trace:
[Info] The "Use Cached Exchange Mode for new and existing Outlook profiles" Group Policy is enabled.
CPUU is designed to temporary disable this policy before logging on to the source mailbox. However, in some environments this policy is kind of "aggressive" and enables itself back right after CPUU disables it and before CPUU manages to log on. Therefore, CPUU cannot log on and fails and rolls a profile update back.