SharePoint Web Part Access Denied error

I have a list in my sharepoint site.The users who have contribute access is able to add items on the list.But recently some users who have contribute access was not able to add new item.The normal work around we do is we will add them to the owners group and ask them to login .Then we ask them to logout and remove them from the owners group and issue will be resolved.But the开发者_StackOverflow proper way shouldn't be like that.Please give the proper way to solve this issue.

The users whom you talk about, Were they added to the contribute group recently? May be the list is not inherting permission(?)

You can use this WebPart (http://accesschecker.codeplex.com/) to check individual acces to every list, lib etc in your SharePoint site.