Install Orion Agent with Invoke-SwisVerb

I am trying to install an Orion Agent with following code.  


Invoke-SwisVerb -swisconnection $swis -entityName Orion.AgentManagement.Agent -verb Deploy -arguments @(
$engineId,`
$agentName,`
$hostname,`
$machineUsername,`
$machinePassword, `
$Ip)

I keep getting this error.  Any ideas?

Invoke-SwisVerb : Password can't be null
Parameter name: password