Hi,
There are changes in the BEx Web Functionality, please see the Document - BEx Versions 3.5 and 7.x after Upgrade
Additional Tipps for the Upgrade see on the BW ALM Page - SAP NetWeaver BW Application Lifecycle Management (ALM)
Furthermore you might re-run the BI-JAVA configuration described in the Document - New Installation of SAP BI JAVA 7.30 - Options, Connectivity and Security
Please Note that you will need a suitable BI-JAVA Stack, if you want to use BEx Web 7.x which means also an 7.3 JAVA Stack
Best Regards Roland