Exchange 2010- OAB not downloading for single mailbox

HI ,

In exchange 2010 environment, one user is not able to download the OAB and getting below error

"TASK USER@DOMAIN.COM REPORTED ERROR (0X80040100F): 'THE OPERATION FAILED. AN OBJECT CANNOT BE FOUND'"

This issue is coming with only one mailbox. When we test the "Test Email Auto Configuration" then test is not showing the OAB URL.

Which exchange attribute we can check

Outlook 2010 is client

issue is coming with cache mode and as well through Online mode

Thanks

jitender