Failed to associate this workflow template with a Microsoft Office SharePoint list

Scenario:
I have been building and deploying my Sharepoint Sequential Workflow with no issues.

Now I started to get following error: output details are as below

Successfully installed this assembly into the global assembly cache: CustomWF.dll.
Successfully restarted Internet Information Services (IIS).
Successfully copied workflow.xml to C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\FEATURES\CustomWF\workflow.xml.
Successfully copied feature.xml to C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\FEATURES\CustomWF\feature.xml.
Successfully installed the workflow template to Microsoft Office SharePoint Server.
Failed to associate this workflow template with a Microsoft Office SharePoint list. Object reference not set to an instance of an object.
Failed to deploy the workflow template to Microsoft Office SharePoint Server.
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========
========== Deploy: 0 succeeded, 1 failed, 0 skipped ==========

Solution:
While I was not to totally find the real cause of the issue but did a workaround to move forward.

Steps:
1. Created folder structure 12\TEMPLATE\FEATURES\CustomWF
2. Moved the feature.xml inside the folder
3. Moved the element.xml inside the folder
4. Build WSP using WSPBuilder

Article:
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