Error 5 - An exception occurred in SMO while trying to manage a service

Hi

I usean instrumentmade by myselfin vb.netusingSMOobjectsto managea mixed groupof about80MSSqlServer (rel. 2005-2008 r2 & 2012)
With this toolIcheckthe status of services,changeservice accountsand their passwords,etc.
A few days ago one serverstarted toreturn anerror when I run the first operationon anyproperty of the objectManagedComputerjust created.

Error: "Error 5 - An exception occurred in SMO while trying to manage a service"

This is my code:

If UserID = "" Then
            '//Use the credentials of current user
                            mc = New ManagedComputer(serverName)
                        Else

                         '// Use the credentials provided by interface

                            mc = New ManagedComputer(serverName, UserID, UserPsw)
                        End If
                        str = ""
       
                        For x = 0 To mc.Services.Count - 1
                            With mc.Services.Item(x)
                                   servNome = .Parent.Name.ToUpper
                                    srvNome = .Name
                                    srvStato = .ServiceState.ToString
                                    srvStartMode = .StartMode.ToString
                                    srvAccount = .ServiceAccount

                                    ........

                                End If
                            End With
                        Next

The instruction mc.Services.Count generates the error below:

smoex = {"An exception occurred in SMO while trying to manage a service."}
    Microsoft.SqlServer.Management.Smo.FailedOperationException = {"An exception occurred in SMO while trying to manage a service."}
    _HResult = -2146233088
    _message = "An exception occurred in SMO while trying to manage a service."
    Data = {System.Collections.ListDictionaryInternal}
    FailedObject = Nothing
    HelpLink = "http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=11.0.2100.60+((SQL11_RTM).120210-1846+)&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.InnerWmiException&LinkId=20476"
    HResult = -2146233088
    InnerException = {"Failed to retrieve data for this request."}
    IPForWatsonBuckets = 1670498764
    IsTransient = False
    Message = "An exception occurred in SMO while trying to manage a service."
    Operation = ""
    ProductName = "Microsoft SQL Server"
    ProdVer = "11.0.2100.60 ((SQL11_RTM).120210-1846 )"
    RemoteStackTrace = Nothing
    SmoExceptionType = FailedOperationException {12}
    Source = "Microsoft.SqlServer.SqlWmiManagement"
    StackTrace = "   in Microsoft.SqlServer.Management.Smo.Wmi.WMIProxy.ExecProcess(Object request)     in Microsoft.SqlServer.Management.Smo.Wmi.WmiSmoObject.EnumChildren(String childTypeName, WmiCollectionBase coll)     in Microsoft.SqlServer.Management.Smo.Wmi.ServiceCol...
    TargetSite = {System.Object ExecProcess(System.Object)}
    WatsonBuckets = Nothing

The server not have problems and the local Sql Server Configuration Manager work fine.

I copied the tool on the server to run itlocally. Strangely, if I use the credentials of the current logged user the tool works

(mc = New ManagedComputer(serverName) )

If I provide explicit the credentials(domain\username and password, but  the same of user logged in the server)is not working 

( mc = New ManagedComputer(serverName, UserID, UserPsw) )

From a remote serverinsteaddoes not workin both modes.

The server configuration:os Win 2008 R2 EE Sp1 , Ms Sql 2008 R2 Sp2 10.50.4321

Anysuggestion ismuch appreciated

Many thanksin advance