If you're attempting to register DFX or FxSound and you are notified that your serial number is illegal or incorrect, there's a few things to try.
1) Make sure you have downloaded the correct version of DFX or FxSound
License keys will only unlock the software for the version which you have purchased. To make sure you've downloaded the correct version, check your license key here.
2) If you have the correct version of DFX or FxSound downloaded and installed, make sure that you are copy and pasting the license key directly from the order email that contained your license key. Often times the O and 0 can get mixed up!
3) If you're still having issues, please submit a request and we will get back to you as soon as we can!
4) If you actually are attempting to pirate FxSound, why don't you just try the free trial instead and see if the product fits your life first? No hard feelings ;D