This form cannot be opened. It is not workflow enabled

I was creating one workflow with simple Association and Task InfoPath forms. Then deployed the workflow as Feature with all the required InfoPath forms with proper workflow.xml settings.
But whenever i tried to associate the workflow with a custom list. The InfoPath form specified for association opened with the following error message as a pop up.
"This form cannot be opened. It is not workflow enabled"
Then it displayed the "The form is closed" message in the screen.

I checked all kind of settings available in the InfoPath form template and couldn't find any settings related to workflows. I also checked the browser compatibility settings, form ids and even the connection libraries used. But nothing worked out...

Finally i was able to fix the problem only by ..

• Create a new copy of InfoPath forms from the form templates.
• Deleted the existing form templates.
• Renamed the newly created copies of the template to earlier name.
• Deleted all the published versions of the form
• Re-published the forms to a new locations with new form Ids
• Pasted the newly published form in the feature folder
• Changed the form Ids in the workflow.xml

I checked the settings again it was having the same settings as earlier. But this time the Association InfoPath form opened correctly without any error. Still i am not clear about what caused the error mentioned earlier.