Unable to retrieve option-set

Hello Guys, 

I am facing a peculiar problem, where I am trying to retrieve the option-sets (Code snippet added below) but I get an error saying "Could not find optionset". 
This only happens on production instance but it works fine on the developer instance. I have verified that the option-set I am trying to retrieve is present in that instance and the solution is published.


var retrieveOptionSetRequest = new RetrieveOptionSetRequest()
                {
                    Name = optionName
                };
                var response = (RetrieveOptionSetResponse)org.Execute(retrieveOptionSetRequest);