Search service that is used in this call does not support updates - the error you see is returned by its Update function.
You have to use another service.
Kind of a side question… Do you know of any batch creating/updating ways I can code? Our company currently has processes that create new quote/order lines via QuoteSvcContract, but that seems to take a while since I have to create each line separately and then call Update(ref quoteTableset) to commit the changes.
That’s probably exactly where the UpdateExt might come in handy. It’s a different type of dataset, but pretty similar. You can build up the quote in the dataset then updateExt it