Fail to add Node to HistoryService

We are receiving an error in our SAP Enterprise Portal 7.4 (NWA) log.    Its says

Fail to add Node to HistoryService

[Exception]

java.lang.RuntimeException: Secuirty error: failed to validate parameter window ID :

at com.sapportals.portal.navigation.HistoryService.validatewindowID(HistoryService.java:464)

at com.sapportals.portal.navigation.HistoryService.addNavNode(HistoryService.java:291)

at com.sapportals.portal.navigation.HistoryService.addNavNode(HistoryService.java:391)

etc.

I don't know what this means.

Or what we should do to stop it "trying" to make a HistoryService..

Or what security to add to allow it to have a HistoryService?

We are running a single node in the portal. And it is in a DMZ part of the network, so lots of restrictions around it, but this message still means nothing to me.

Ruth Jones