"But when I try to limit it to a particular set the query ends up putting in a lower case ‘S’ for set which is the standard protocol but to list the records in your sets it needs a capital S. The lower case ‘S’ ends up throwing up an error because your OAI feed requires it to be a capital S."
set argument should have lowercase 's':
"But when I try to limit it to a particular set the query ends up putting in a lower case ‘S’ for set which is the standard protocol but to list the records in your sets it needs a capital S. The lower case ‘S’ ends up throwing up an error because your OAI feed requires it to be a capital S."