When using ShareScan 5.4 SP2 to upload to SharePoint 365 the following message appears in the Windows Event Viewer and ShareScan Trace files:
"The operation you are attempting to perform is not allowed because otherwise the list view threshold set by the administrator is exceeded"
This is a message from SharePoint Online. Please see suggested resolution from Microsoft, below.
"When you view a SharePoint Online list in Office 365 Enterprise, you receive the following error message:
The number of items in this list exceeds the list view threshold, which is 5000 items. Tasks that cause excessive server load (such as those involving all list items) are currently prohibited.
Please see the Microsoft KB: