1GB SD Card difference

I have and application that I have used the Sandisk 1GB SD card. I recently purchased a new group of Sandisk 1GB SD card that look the same with the exception they do not have a “HKT” sticker on them like the original. The new cards will not function in my existing application. What does the “HKT” sticker identify? I would like to know if this is a cause for these cards to not function with my application now?