Add Additional Aliases to existing Distribtion groups Exchange 2010

Hi Guys,

I have a number of distribution lists that I need to add an additional email address to for a secondary domain.  I tried this -

import-csv "D:\pst\company\import\distalias2.csv" | foreach {get-distributiongroup $_.distalias -organization company | set-distributiongroup -emailaddressses @{add='$_.alias1'}}

the $distalias is the name of the distribution group and the $alias1 is the email address I am trying to add .

I get the following error

A positional parameter cannot be found that accepts argument 'System.Collections.Hashtable'.
    + CategoryInfo          : InvalidArgument: (:) [Set-DistributionGroup], ParameterBindingException
    + FullyQualifiedErrorId : PositionalParameterNotFound,Set-DistributionGroup

Can someone please point me in the right direction?