"File not found" error when you open target site.

Issue:

The migration completed successfully with no errors, but when you try to open the target site you receive the File Not Found error:

 The problem is that the master page of the target site (e.g. default.aspx) points to the wrong page layout. This happens because it links to a layout which does not exist in the target site collection. Usually it happens when master page is inherited from the parent site but you migrate the child site only.

Example:

You have http://source/test sub-site whose default.aspx page is linked to a custom master page “Custom.master” located in the top level site.

The target site collection (http://target) does not have the "Custom.master" page. When you migrate the sub-site under the target site collection, you receive the error when open the target site. 

You should copy master page from source to the target manually using SharePoint Designer.

To find out which master page is used:

1. Open the migrated target sub-site in SharePoint Designer.
2. Open default.aspx. The master page relative URL is written in the top level corner:
   

Note: The URL above means that the master page is located in the site collection master page gallery.


To copy the master page:

1. Open the source site collection (http://source) in SharePoint Designer and move to the _catalogs/masterpage
2.  Copy the Custom.master page
3.  Open th target site collection in SharePoint Designer and copy the master page to the _catalogs/masterpage

When the master page is copied you can successfully access target site.