button has no properties (js error)

I got this javascript error when I reach the edit mode of a node type containing two image fields.

Do you think it's a ordering .js' file problem?

Fact:

1. CCK version : 5.x-1.6-1
2. imagefield version : 5.x-1.1
3. permissions for your tmp and files directory : ??? but image upload correctly.
4. download method (public or private files) : Public
5. imagefield configuration : two on the same node type (one with multiple value)
6. expected results : no more js error
7. the unexpected actual results :

button has no properties
redirectFormButton("http://localhost/Drupal/upload/js", undefined, Object button=#attach-button wrapper=#attach-wrapper)drupal.js (line 31)
jsUpload("http://localhost/Drupal/upload/js", "attach-button", "attach-wrapper", "attach-hide")upload.js (line 27)
uploadAutoAttach()upload.js (line 14)
e([input#edit-attach-url.upload http://localhost/Drupal...], function(), undefined)jquery.js (line 2)
e(function(), undefined)jquery.js (line 2)
uploadAutoAttach()upload.js (line 7)
e()

8. Steps to reproduce the problem : access the edit page of the node type.

Thank for your attention!