Existing packages containing Lookup Plus component and designed with SSIS+ 1.5 or older version are incompatible with SQL 2012. To have successful upgrade follow these steps:

• Install SSIS+ 1.6 or newer on a machine where you have existing packages designed with SQL 2005 or 2008.
• Open the existing package containing Lookup Plus component and re-save.

The saved package will now contain SQL 2012 compatible data and the package is ready for upgrade.