SSMS Add-in - I can't get the existing Connection, can somebody help me?

Every time I try to use the "ServiceCache.ScriptFactory.CurrentlyActiveWndConnectionInfo.UIConnectionInfo"
or the "ServiceCache", I get the same message:

"The type 'Microsoft.SqlServer.Management.UI.VSIntegration.ServiceCache' exists in both 'SqlPackageBase.dll' and 'Microsoft.SqlServer.SqlTools.VSIntegration.dll'"

Somebody please help.