You will typically receive the following error while running a pdf report, when the display is not working properly.
Xlib: connection to "myhost01:0.0" refused by server
Xlib: No protocol specified
REP-3000: Internal error starting Oracle Toolkit.
REP-3000: Internal error starting Oracle Toolkit.
If you need to change the display setting:
a. OAM->Sitemap->Autoconfig-><CONTEXT_NAME> (Applications Tier) ->Edit Parameter-> Environments->oa_environment:generic_service->X11 Display- s_display>Myhost01:1.0
b. Run autoconfig at middle tier.