Messages of this category can state different errors. Some are:
In these cases SYNCING.NET can't access a specific internal file correctly. We have experienced that the following circumstances may be related to these effects:
If you encounter duplicate folder names within the SYNCING.NET "Outlook Group" configuration on one of your computers, then delete these folder selections, restart SYNCING.NET and re-add the concerned folder to the synchronisation. Please mind to add the folder on that computer which holds the current data set.
If there are no duplicate folder names, you may check your system components regarding possible issues.
If these actions do not solve the issue, we recommend to remove, then reinstall the concerned "Outlook Group(s)" and monitor the issue.