You've not stated how you're trying to transfer them. I assume that you've got the media card inserted into a card reader. If so, the standard technique (or, more accurately, one of the standard techniques) for copying them across is as follows:
In 'My Computer', double-click on the icon representing your media card. If the window opens 'full screen' (or just very large), resize it (by dragging the edges of the window) so that it only takes up pert of the screen.
Then navigate to the folder (e.g. 'My Pictures') where you've stored the scan files. Once again, resize the window, so that you've got the two windows side by side on your screen.
In the window displaying the folder where your files are, highlight all of the relevant files. (If you want every file in the folder, go to Edit>Select All. If you want a block of files, click on the first one, then hold down Shift while clicking on the last one. If you want several individual files, hold down Ctrl as you click on each one).
Then simply drag the group of files (by clicking on any one of them and keeping the button held down) across to the window which displays the contents of your media card.
If you've tried this method, and it doesn't work, please post again (on this thread) telling us what's going wrong.
Chris