SD Card Problem in Slot

I just got a digital photo frame as a gift.
So I picked up a 2 GB SD card to store the pictures on.

I use an SD slot in the PC to write to the SD card.
The first time I copied around 150 pictures (JPGS) which used up around 10MB.

I'm trying to copy more pictures to it but it is giving me the message 'Error Copying File or Folder' the directory or file can not created.

The SD card has 1.9 GB of space left on it. If I delete a picture from the SD card then I can copy a new picture to it. It also won't let me create a folder on the SD card.

I'm running windows XP (Pentium 4).

Any ideas why it won't let me copy any more pictures onto an SD card with almost 2 GB of space on it ?