Error 5100 data protector express 4.00-sp1

[Fabio D'Angelo]

Data Protector Express Version 4.00-sp1 (build 43064) on windows server 2003 32bit up to date with service packs and other update.

After backup job runs the report shows this error:
Errore 5100: Infrastruttura del sistema di snapshot non riuscita

In English sounds something like this:

Error 5100: Snapshot infrastructure doesn't work.

Data protector service runs as local service.

What I have to do?

Thanks!
Fabio