BIA uses JDBC to connect to the Cúram database(s), in order for this to work the appropriate JDBC driver needs to be available inside iServer. The process for installing JDBC drivers in general is described in the "Deploying BIRT reports to BIRT iServer" manual, supplied with BIRT iServer, for convenience the step required is listed below:
Copy the appropriate (Oracle or DB2® as required) driver jar files from $CURAM_DEVELOPMENT_HOME\CuramSDEJ\drivers to $ACTUATE_HOME\iServer\Jar\BIRT\platform\plugins\org.eclipse.birt.report.data.oda.jdbc_XXX\drivers (where XXX is the version number, for Actuate iServer 11 SP1 this is 2.6.2.v20110326-0603)