SharePoint - How to fix the error whn two users are approving the same item

Hi,
i have a workflow in sharepoint designer 2010 and when two different users are going to approve the same item,  the first user who approve it 1 sec before the second user is ok, but the second user does not know that the item is approved and when  attemp to do this an error page is showing?
how can i avoid the error page and show any message ?
i developed workflow with sharepoint desigenr 2010

thnx

Hello,

the best way to avoid this problem is maintain versions of your doc.specify whether new items or changes to existing items should remain in a draft state until they have been approved.

here is a LINK, completely talks about this.

Hope it helps!!
Regards
D