Data card lost all it data

I don't know how it would have "lost" all it's data. More likely is all of it's data was "erased" or "deleted".

Take the card out and put it into your computer or someone else's Iway and see if the file folder is still on there. It probably is. You might just need to reset your Iway. You also might try downloading the newest software update (ver 1.3) from the Lowrance website. http://www.lowrance.com/en/Products/Automotive/iWAY-250C/Downloads/iWAY-250C-Software-Update/
This is not the maps, it's just the software for the unit itself.

If the map file actually isn't on the card anymore, then ask yourself:
Did you make a data card backup to your computer like the user manual suggests?
If yes, put the backup file onto a 2GB SD card and stick it back into your Iway.
If no, then you're out about $90 to buy a new set of maps. They come from Navtec, you can't buy them from Lowrance because Lowrance doesn't produce them.
Good luck