RSBOLAP 018 Error In WAD

Hi Experts, i am using BI 7.0. And am trying to execute reports from WAD. However it always gives an error saying

"RSBOLAP 018 Java System Error: An unknown error has occoured during portal communication" while opening the report and

"RSBOLAP 018 Java System Error: Incoming call not authorised" while executing the report.

I read SAP Note 937697 and executed the support tool to receive the following error.

RED: BI Mastersystem

Error: Error while connecting to BI mastersystems via RFC. java.lang.RuntimeException: Native connection to banckend system is broken

Solution: Check connection properties in Portal Systemlandscape category 'Connector' (Systemlandscape / SAP_BW)

I checked on the same...and all seems correct...also the connectivity tests in the BI Portal pass

Please help