It seems that Central Admin is installed on separate server. To resolve the issue you need to register Virto product .dll file in GAC on Central Admin server.

To do it please do the following.

1) Copy Virto product .dll (let it be Virto.SharePoint.Product.dll) from WFE server GAC to Central Admin server (let it be folder c:\Temp).

2) Run as administrator power shell on Central Admin server.

3) Execute the following script in power shell

Set-Location"c:\Temp"

For SharePoint 2013:

[System.Reflection.Assembly]::Load("System.EnterpriseServices, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")

For SharePoint 2010:

[System.Reflection.Assembly]::Load("System.EnterpriseServices, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")

$publish=New-Object System.EnterpriseServices.Internal.Publish
$publish.GacInstall("c:\Temp\Virto.SharePoint.Product.dll")
iisreset

Additional license is not required for product on Central Admin server.