WBS renumbering

[natalia]

Hi,

I've posted this question before and got no answer so,
here it is again in the hopes that someone can help...

Would anyone know why in a specific file I cannot renumber
the WBS for selected tasks only? The option is there but
it is greyed out. However, on all my other files, the
option is available.
Do I have something specific set up that does not allow me
to select the option of renumbering selected tasks?

Thanks!

Natalia