A little more detail:
Interplay goofed and shipped some EAW CDs with a 4x4 CD-key pattern.
Unfortunately, EAW uses a 5x4 pattern. Orion Pirates (OP) uses the 4x4 pattern, and we believe (unless I happened to miss the post confirming) that Interplay put OP key codes on EAW cases...
Hence Cleaven's remark, of getting a (backup) copy of OP to use the legitimate OP keycode you received with your EAW disk. Unfortunately, the supplier of legitimate EAW keycodes (Interplay) is hard-to-reach these days...
The fun thing, you can download copies of the original EAW campaigns and play them on OP. I haven't played EAW single-player in ages, and haven't played EAW's D2 since the last main campaign there...