The Large List Selector control has been updated with additional security enhancements.
During migration, LargeListSelector.controls.cs (.vb) and FvLlsHyperlink.cs (.vb) are replaced with new files. Any customizations you have made to these files will be lost. These files are located in:
...\<Application Folder>\App_Code\Shared\LargeListSelector.controls.cs (.vb)
...\<Application Folder>\App_Code\Shared\FvLlsHyperlink.cs (.vb)
After migration, re-apply any customizations you may have made to the original LargeListSelector.controls.cs (.vb) and FvLlsHyperlink.cs (.vb) files to the new files.
Version 5.1 Application Migration