Hello. My name is***** can help you with your question.
I believe you're talking about and SD card and the one you mentioned is 4 GB and not 4 MB as you originally put?
It sounds like the card you're putting in is an embroidery card. Is that correct? If so, and if it's no longer working, I do believe brother will replace it under warranty. So I would check with them first. Replacing the card with a new one is what you will have to do ultimately but it would obviously be best if you can get it covered through brother under warranty.