Exception calling "Remove" / Bad variable type when removing SiteGroup with PowerShell

Hello,

I am trying to remove all site groups in a site collection through Powershel by using the $Web.SiteGroups.Remove() function.

When doing so i get the following exception:

Exception calling "Remove" with "1" argument(s): "Unable to cast COM object of type
'Microsoft.SharePoint.Library.SPRequestInternalClass' to interface type 'Microsoft.SharePoint.Library.ISPRequest'. This operation
failed because the QueryInterface call on the COM component for the interface with IID '{BDEADF28-C265-11D0-BCED-00A0C90AB50F}' failed
due to the following error: Bad variable type. (Exception from HRESULT: 0x80020008 (DISP_E_BADVARTYPE))."
+                 $sitegroups.Remove($sitegroup)
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : InvalidCastException
 

My code is the following:

$webapp = Get-SPWebApplication http://workdev.contoso.local

$allsites = Get-SPSite -WebApplication $webapp
foreach ($site in $allsites)
{

            $rootweb = $site.RootWeb;
        $sitegroups = $rootweb.SiteGroups;
            foreach ($sitegroup in $sitegroups)
            {
                $sitegroups.Remove($sitegroup);
            }

}

I have tried it as well with RemoveByID with the same outcome. The SiteGroups are properly read and listed only the Remove just doesn't work. I have tried also to call the command with ToString() but no luck.

Any help is appreciated!

Thank you in advance,

Ioannis