Problem with index directive (2)

["tecnico" <tecnico@rdi-net.com>]

(Sorry, I beliave that I send this mail cut before)!!

Hy, I'm trying config an OpenLDAP server, but I have some problems with
index directive.

I try to maintain an index of some attributes, for example:
index cn,sn  pres,eq,sub
index telephoneNumber approx
but the slapd daemon returnd errors like this
line 67: substr index of attribute "telephoneNumber" disallowed

What is the problem?

Thanks for all!
Bye