If you are using the community edition of Sitefinity, you will most likely encounter the 404 error as the module is not included in that edition of the CMS.
The migration module is included in all editions of Sitefinity except for the community edition ( that includes the SBE, SE, PE, EE ).
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items