Level-1 backup after level-0 using ontape

Hi! I use ontape -s to create archives in order to perform backups. I don't really use any tape device to make the archives. Instead, I have LTAPEDEV pointing to the path of a Unix flat file. So, my archives are not segments of tape, but Unix files, one per archive. This schema used to work very well when we had Informix version 7.23. But a problem showed up once we moved to version 7.3: I type ontape -s -L 0 to perform a Level-0 archive. The archive is created successfully and the archive is registered (In onmonitor, the archives register is shown by selecting Status and then Archive). Then, the next day I type ontape -s -L 1 to perform a Level-1 archive. But, even though I see that the level-0 archive was registered, the system displays the following message after I entered the command: Archive failed - No level 0 archive exists; only level 0 archive is allowed. Program over. What could be wrong? What could have changed in the transition from the older version to the newer? I will appreciate any help on this. Thanks.