The BaseApplicationPage.cs (.vb) file is updated to fix a set focus problem and code and to enable multiple languages in SharePoint applications.
BaseApplicationPage.cs (.vb) is replaced during migration.
After migration, re-apply any customizations you may have made to your application’s original BaseApplicationPage.cs (.vb) file.
For web applications, this file is located in:
…\Shared
For web sites, this file is located in:
…\App_Code\Shared
Version 7.0.1 Application Migration