The CA Business Intelligence is a big application with several components/services. Sometimes it does not uninstall/ remove those component properly and re-installation becomes difficult.
IMPORTANT: This article contains information about modifying the registry.
Before you modify the registry, make sure to create back up of the registry and ensure that you understand how to restore the registry if a problem may occur.
For more information about how to back up, restore, and edit the registry, please review the relevant Microsoft Knowledge Base articles on support.microsoft.com.
First of all we have to ensure we followed the CA Business Intelligence Installation Guide, Chapter-3, Section: Uninstall from Microsoft Windows.
If that does not help then we can review and try the following:
Business Objects "Uninstall Procedure (manual)"
NOTE: Above is strictly for the installation applicable for CA Business Intelligence bundled with R12.0 GA version. And you need to follow exact same order of bullets as mentioned.