hi, I'm getting this exception when trying to execute an script

exception : Access not allowed.(Code: 0x80070005) Skyline.DataMiner.Net.Exceptions.DataMinerSecurityException: Access not allowed.

The function that fails is this:

private static string GetServiceElementParameter(Engine engine, int dmaID, int serviceID, int parameterID)
{

try
{
GetParameterMessage serviceParameter = new GetParameterMessage(dmaID, serviceID, parameterID);

GetParameterResponseMessage parameterMessage = engine.SendSLNetSingleResponseMessage(new GetParameterMessage(dmaID, serviceID, parameterID)) as GetParameterResponseMessage;

if (!string.IsNullOrEmpty(serviceParameter_response.DisplayValue))
{
string paramValue = serviceParameter_response.DisplayValue;
return paramValue;
}

return null;

}
catch (Exception ex)
{
engine.GenerateInformation("exception : " + ex.Message +ex );

return null;
}
}

This is the line that throws the exception. I think it must a stupid error but I'm new at this

thanks