When performing a migration, Sharegate displays the following error:

SharePoint encountered an error related with property promotion/demotion. This is often caused by copying an Office file that is either corrupted or in an old format.

This error occurs when SharePoint is unable to open the Office files (such as Word, Excel, etc.) that are being copied. The reason why SharePoint is trying to open these files is that there is a feature called property promotion/demotion in SharePoint that automatically synchronizes properties from Office files to SharePoint (promotion) or from SharePoint to Office files (demotion). Every time an Office file is uploaded, SharePoint will open it to read its properties and set them in the SharePoint library columns. Conversely, every time properties are updated in SharePoint, it will open the Office file to update the properties within the file.

When Sharegate migrates files, it always uploads them first and then updates their properties. If those files are Office documents, it will automatically trigger the property promotion/demotion within SharePoint. When SharePoint is unable to open the file (for example, it could be an old version of Office or the file could be corrupted), it gives an error which prevents the copy to work as expected.

There are 2 approaches that you can use to resolve this issue: