Cannot connect to the olap source problem

Hello,

When am trying refresh a report . its failing when am not actively logged on the the BI Launchpad. but its running when am logged into a session at that time.

failing to run in background with a error message: Cannot connect to the olap source com.businessobjects.mds.olap.OlapException: [Internal] SSO token or User password is empty. [Internal] SSO token or User password is empty.

however the same is running successfully if we are logged on at the time it was scheduled for.

any ideas ??

BOE R 4.1

datasource  bw olap

Many Thanks,