When performing a migration, Sharegate displays the following error:
There was a problem contacting the Server Extension. This is often due to the resource usage quota being exceeded on the site collection where it is installed, or to an installation problem with the server extension.
Any error code ending with: -051
This error can occur for multiple reasons, and depending on the case, it can be difficult to assess without investigation.
If you are migrating to Office 365:
You might see this error when using an older version of Sharegate.
The Sharegate server extension for SharePoint Online is a sandbox solution. In November 2016, Microsoft deprecated sandbox solutions. Sharegate worked with Microsoft to make the necessary changes so that Sharegate no longer requires a sandbox solution to migrate to SharePoint Online (Office 365) for any case.
Please update Sharegate so you do not need to activate the Sandbox solution anymore. If you still have it activated in your environment, you can deactivate and delete it.
If you are migrating On-Premises:
You will need to contact the support team, who are familiar with the possible solutions to this issue depending on your specific case, and will be happy to help.