"This is a frequent answer, but unfortunately it is not correct."

Translation: Ez egy gyakori válasz, de sajnos nem helyes.

[richardkiss]

Is it incorrect to leave out the "egy"?

[vvsey]

It is optional, it can be left out.

[ctangsgaard]

I used "hanem" instead of "de" but that was wrong. How can I know which one to use?