The BI 4.2 SP04 version of SAP Dashboards produces the following error when attempting to add InfoBurst dashboard connectors:
The Add-On you are trying to install is not valid.
This issue is under investigation.
SAP has confirmed this is an issue and will be fixed in BI4.2 SP04 Patch1. As a work around if you copy the .xlx file to Xcelsius install folder (C:\Program Files (x86)\SAP BusinessObjects\Xcelsius 4.0) and then add the addon from there it will work.