Hello,
You're receiving this message because you're trying to flash a "too recent" firmware (FW) version. In short, older firmware version does not recognize the newest versions, thus blocking the update.
There are a few options on how to go about this:
Option A - installing the newest firmware via bootloader:
This option may seem a little scary, but this is quite easy. First, download the desired FW version from Wiki. Make sure to select the correct device! Then simply follow the instructions laid out here: https://wiki.teltonika-networks.com/view/Bootloader_menu
Option B - install the latest firmware that the router recognizes, and install RUT9XX_R_00.06.09.2 from there:
I'd not recommend this, as it will take quite a bit of time, but it's possible to do an intermediate "jumps" between versions. I cannot tell you exactly which version to try to install, but I'd recommend updating to RUT9XX_R_00.06.05.x and then trying to update to RUT9XX_R_00.06.08.2 and finally to RUT9XX_R_00.06.09.2.
Attention!
FW version RUT9_R_00.07.00 and above will not be supported on legacy-design (RUT955 *7V***) devices.
Best regards,
Daumantas G.