Error when install avast in silent mode

Hello, I try to install avast from command line with silent switch “avast.exe /verysilent”, but receive this msg:

“you need to pass in a single character to the /brandcode: flag, e.g. /brandcode:Z”

Avast is installed, but is a bit annoying, how I can remove that message?

This “problem” only occurs with the new version (6.0.1289), old versions OK.