Error when trying to change product key

Hi all

I am trying to change the product key on a Exchange 2010 Server from an Standard edition to an Enterprise Edition. I run the command "Set-ExchangeServer -<servername.domain.internal> -ProductKey XXXXX-XXXXX-XXXXX-XXXXX-XXXXX -DomainController dc01.domain.internal".

Then I get the error "A positional parameter cannot be found that accepts argument '.domain.internal'".

Any clues? I have tried any different combination I can think of but still got that annoying error. 

Pittbull