If you got an error message ‘Could not open file’ – saying the file was corrupt or has a wrong extension (due to the network failure or disk space issue when you previously saved the file) you should be able to retrieve an earlier version, saved as backup.
When Omniscope saves "MyFile.iok", it creates a backup of the previous file first, which is usually next to the file and called "MyFile (backup).iok" or "MyFile (backup 2).iok". If you find this, it should be good to use.
Otherwise, if it is unable to create that backup, e.g. due to insufficient disk space, it creates a backup in your system temp folder, called "visokio_temp_tempres*.iok" (likely alongside many other Visokio temp files) where * is some unique auto generated value. You may need to search by timestamp to find the right file.