An error has occured in Approval

I think, Workflow is the easiest part of SharePoint for anybody to use and especially the out-of-box workflows. Yesterday, One of the user in my project reported an error regarding workflow. The scenario was he set an approval workflow for himself and when he tried to approve it then he got an error message as follows:




When we set up an workflow for the document library and list, We usually follow these process :

-Go to Settings->Workflow Settings->Add Workflow
-Choose the Approval workflow from the list, make it start on item creation go to the second workflow page.
-Select the approvers asper your requirement and check "Update the approval status (use this workflow to control content approval)"
-Finish and the workflow has been set !!

And now the mystery begins and you will get an error as mentioned above. and now You will ask,why? So the keyword is "Approval" !!

This is an approval workflow which should among getting the approvals update the approval status of the document so, if you missed one tiny little step like setting the approval for the document library this simple task will fail at the end.

Resolution:-
-Just go to the document Library Settings
-Versioning Settings Page
-Set "Require content approval for submitted items to?" to yes and everything should be fine.

I hope the above information will helps you to overcome the above mentioned error message!!
Thanks!!!