This agent doesn't work when I edit the document

Hello,

I have a field “AssignedTo” for which the user need to select a name in the NAB. I use this topic http://www-10.lotus.com/ldd/sandbox.nsf/Threads/EFE6B2307D3CD5C985256D9C0062B0D7?OpenDocument

It works correctly for a new document but not when I edit an old document and want to select a new name for this field.

I get the error message :

Error 500 - TTP WEB Server : Invalid URL exception.

Could anyone help me ?

Thanks in advance