When attempting to copy an item, Sharegate displays the following error:
Sharegate was unable to find the user "username" through the people picker. This can happen if you are using a custom people picker. Please ensure that you are using the out-of-the-box SharePoint people picker.
When migrating an item, Sharegate will try to find the user named "username" on your SharePoint server. To accomplish this process, it uses the people picker of SharePoint. The people picker is the built-in page used by SharePoint to allow end users to search for users and groups. This page can be customized, but if it has been modified too much, Sharegate may be unable to use it effectively to search for users or groups. As such, Sharegate may raise the preceding error.
You need to validate that you are using out-of-the-box people picker. It should have the following look in SharePoint 2010 :
If you seems to have the out-of-the-box people picker, please validate that you are able to use the people picker on your SharePoint server.
You could simply connect yourself to a site collection on your server, then create a custom list in which you will create a column of the type Person or Group.
Add an item to your freshly created list and ensure that you can use the people picker for the column created previously.