The error is because two files were specificed for the backup. This is commonly by mistake, where there were two files listed in the destination box on the backup dialog when that backup was made. The backup doesn't go to the latest added or to the highlighted one, it's stripped across both and you need both files to restore. There's no way to restore with only half a backup as you only have half of the database there.
If you have a backup of MSDB from before the reinstall, restore that and look at the backup history, it'll tell you want files the backup was striped across. Not sure if the info on which files the backup was striped across is part of the backup header.
RESTORE LABELONLY might give you more info, but I don't think it'll tell you where the other file is.
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