Call ps1 file from C#

Hello All,

I am having a power shell script file which needs to be called from web service. While executing power shell commands from file , its showing following error :

The term 'New-SPAuthenticationProvider' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.

C# code is as below :

private static void RunPowershellScript(string scriptFile, string scriptParameters)
        {
            RunspaceConfiguration runspaceConfiguration = RunspaceConfiguration.Create();
            Runspace runspace = RunspaceFactory.CreateRunspace(runspaceConfiguration);
            runspace.Open();
            RunspaceInvoke scriptInvoker = new RunspaceInvoke(runspace);
            Pipeline pipeline = runspace.CreatePipeline();
            Command scriptCommand = new Command(scriptFile);
            Collection<CommandParameter> commandParameters = new Collection<CommandParameter>();
            foreach (string scriptParameter in scriptParameters.Split(' '))
            {
                CommandParameter commandParm = new CommandParameter(null, scriptParameter);
                commandParameters.Add(commandParm);
                scriptCommand.Parameters.Add(commandParm);
            }
            pipeline.Commands.AddScript("Add-PSSnapin Microsoft.Sharepoint.Powershell");
            pipeline.Commands.Add(scriptCommand);
            Collection<PSObject> psObjects;
            psObjects = pipeline.Invoke();
        }

What might be the issue.

Your help is appreciated.

Thanks in advance.