JPivot export excel HTTP Status 404 how to view log?

As in title, I have a bi-server 5.0.1 CE and I did a Jpivot that work well.
When I try to print it or to export to excel it gives the error HTTP Status 404:
HTTP Status 404 -

---

type Status report
message
description The requested resource is not available.

---

Apache Tomcat/6.0.36

have you any idea why it happen and where to find the log?
Thx!