How we check the errors before running the report, Plz let me know the answer? | Cognos

Before u run a report. U have an option called 'valididate report' in run menu..
Then u can find the errors what u made.
Actually we are migrating one project to ACTUATE business intelligence solution to COGNOS
REPORTNET? why the client want to migrate from ACTUATE to COGNOS REPORTNET?