Problem with permission of one special user

Hi

I have 2 sharepoint list: list 1 and list 2.

When users with contribute permission add items to list1, the workflow was started and create item in list 2.

I create sharepoint group and grant contribute permission for this group to list1 and list2 . workflow will completed when all member of this sharepoint group add item to list 1,except one user.

One user when add item in list1,the workflow can't be completed and give error related to permission. I check permission of this user in site permissions, he has contribute permission in all sharepoint  site.

What's wrong and what things should I test for this problem?

Thanks.