NintexWorkflowID error

One fine day, when I tried to save the newly created Workflow, I saw the below error. We searched many Site, Forums, blogs, but was unable to find the Solution for this.

Issue:

Server was unable to process request. ---> Could not find field NintexWorkflowID on NintexWorkflows library.

We retracted the Nintex Solution and Redeployed. We also de-activated the Feature on both Site Collection and Site. Uh.....didn't work. Finally found the Solution.

Solution: 
We found that few fields are missing in the Nintex WorkFlows Library.

To go to Nintex Workflows Library, add NintexWorkflows/Forms/AllItems.aspx to your site as shown in below example.

For Ex: The URL would be http://devtest.dev.com/sites/devtest/NintexWorkflows/Forms/AllItems.aspx

Go to Document Library Settings. I don't know how and why, but found the below fields were missing. 

We need few Tools from Nintex to verify the usage of Nintex and find if we have any duplicate fields.

NOTE: Use this URL at the Site level to view all Nintex Wokflows available in the site >> http://devtest.dev.com/sites/devtest/_layouts/NintexWorkflow/WorkflowGallery.aspx