During startup of warm standby database '%1!s!' (database ID %2!s!), its standby file ('%3!s!') was inaccessible to the RESTORE ...

During startup of warm standby database '%1!s!' (database ID %2!s!), its standby file ('%3!s!') was inaccessible to the RESTORE statement. The operating system error was '%4!s!'. Diagnose the operating system error, correct the problem, and retry startup.