Stopping website with powerShell script

Ive got a script for stopping a site:

param($HostName = "localhost", $SiteName)

$server = $HostName
$siteName = $SiteName
$iis = [ADSI]"IIS://$server/W3SVC"
$site = $iis.psbase.children | where { $_.keyType -eq "IIsWebServer" -AND $_.ServerComment -eq $siteName}
$site.start()

# SIG # Begin signature block ...

But when i run the script on a server with high security policies i get this error:

The following exception was thrown when trying to enumerate the collection: "Unknown error (0x80005000)".
At D:\DeploymentScripts\Common\StopSite.ps1:6 char:8
+ $site = <<<<  $iis.psbase.children | where { $_.keyType -eq "IIsWebServer" -AND $_.ServerComment -eq $siteName}
    + CategoryInfo          : NotSpecified: (:) [], ExtendedTypeSystemException
    + FullyQualifiedErrorId : ExceptionInGetEnumerator

From what I have read this might occur if i don't have access to the IIS , but im running the script as admin, should that not grant me the access i need ?

Does the webadministration module give more access rights ? I don't import this since i didn't have to do this on the other servers, if i need to import the webadministration there is another problem, when i try i get a error saying the WebAdministrationAliases.ps1 is not digitally signed...

I have tested the script on other servers with no problem, but this one got more strict policies as mentioned above, and its not a option to change the policies.

Im running this on a Windows server 2008 R2, with IIS 7.5.

Import-Module WebAdministration
Stop-WebSite 'Default Web Site'
Start-WebSite 'Default Web Site'