Unable to connect to service WebiPlugin.WebiSession

I am getting the following error when running a publication of a web intelligence document:

2013-04-05 10:26:06,420 ERROR [PublishingService:HandlerPool-30] BusinessObjects_PublicationAdminErrorLog_Instance_1651907 - [Publication ID # 1651907] - Scheduling document job "REPORT" (ID: 1,653,987) failed: Unable to connect to service WebiPlugin.WebiSession from server BOSERVER.com:6400 via CMS osca:iiop://GRZSMS185.andritz.com:6400;SI_SESSIONID=1653977JpB38w9BrGXJIf0opXpgAS1 (FWM 01006)

we are using 3 nodes. We always have a lot of problems with publications in BO 4.0 (latest patch level), but we sized the nodes properly.

Any ideas what the error could mean?