[ZOPE] : problem with Tree tag

hi, I am using ZOPE for my project. Actually I have to display the employee hierarchy in my page whose ever required. For that I take the Emp_no. in the first page and when I submit the form it will go to the next dtml method in which I call the tree tag. It will work fine in the first page. If I try to expand the tree by clicking the PLUS sign it will give error. Key Error: Emp_no. Can any body help me. thanks in advance. subrahmayan.