This can happen either because the version you are trying to update from is too old, or the version of the Red Pitaya OS is incompatible with the base Linux that is running on your board.
Here's how to solve this. You can manually update both at the same time and avoid lengthy procedures. Another advantage of doing this is the simplicity of the process.
Of course, as always, the first step would be to make a backup if you have some saved work on the unit, or simply use a different micro SD card. Please make sure to update the web user interface after installation, since some things can be cached from the previous version and this can lead to unpredicted behaviour.
We recommend you to always update manually to our latest Beta OS, it works smoothly and it has all the latest features implemented and the reported bugs fixed.