I was experiencing this problem as well, just follow these simple steps to fix it.
this is copied from the common answer post stickied under the technical support section, posted by bbr_insuw.
============================================================ Error message: data file has corrupted ============================================================ Steps to fix data corrupted message...
1 - Navigate to your navyfield install directory (usually c:\program files\sd enternet\navyfield)
2 - MOVE all the files you find ending in ".data" to another folder, your desktop, or where ever.
3 - Start navy field. The updater will download the missing files and then when the game tries to start will give you an error with one of them (usually yf.data).
4 - Copy the data file it is complaining about back into your install directory from wherever you moved it.
5 - Start the game again. This seems to work for most users experiencing this issue now. If it DOESN'T work for you, the next thing to try is the DATA FILE DOWNLOAD followed by the PATCH DOWNLOAD on this link... http://navyfield.com/Download/Game/Main.aspx And if THAT doesn't work, you might have to reinstall the whole dang game. if that happens, we'd love to hear about it.