Resolved for me !
I have found my problem :
1. Open the template
2. Open the Workflow scripts
=> Dialog Box is displayed
"This template project was created based on another project. In order to make your workflow available for projects linked to that template, you should convert your workflow scripts. Click 'Yes' to start converting your scripts.
For more information, see HP Software-solve knowledge base article KM494331"
KM494331 is "How to use the convert tool in Quality Center"