Hi, I am trying to update the firmware of this router:

Firmware Version:    
3.18.1 Build 191217 Rel.65341n (BETA)
Hardware Version:    
WR940N v6 00000000 (BETA)

But I get this error.

Error code: 18005
Upgrade unsuccessfully because the version of the upgraded file was incorrect. Please check the file name.

I have tried both versions (US) and (EU), and different numerical versions, all with the same result