Ancient wonders usually can only be built in the ancient and classical age (in this case maybe even the medieval age). After you research Divine Right, I think you have enter the Renaissance age, which disable your ability to build those ancient wonders
not exactly. i'm sure it's not exactly that when you yourself reach a new age, you can't build an ancient wonder. i'm not sure which of two reasons is why:
1) it might be that the wonders are restricted to eras only as far as game start eras. that's my real guess. the wording in the civilopedia for the pyramids is "can only be built on classical and earlier
starts", it doesn't say can only be built before classical era ends, if i'm making sense.
2) the current era of the
world as a whole is not necessarily the same as the era that you are in; you yourself being in renaissance doesn't mean that that the game thinks the world has entered the renaissance era. quoting from somebody who knows way more about that than i do, "Current game era is considered to be the average era of the remaining players, rounded down, with ancient being considered '1', medieval '2', and so on." so if infantry#14 is right and you can only build wonders in their own eras, my example below proves that in at least vanilla, it's the "game era" that obsoletes the wonder not your own era.
as far as the oracle itself, it's a "classical start or earlier" wonder. i played a game in Vanilla (you're in warlords so may not be the same) on Chieftain where my goal was ASAP diplo victory, so i beelined mass media. the AIs were slow, this was chieftain. i delayed oracle a very long time, in fact until i was 1 turn away from liberalism. i was no longer in the classical era myself, but the AIs were. i picked radio from the oracle and mass media from liberalism, it was hysterical fun.
so in 1.61 vanilla, i'm sure you can build the oracle when you're post-classical, at least if the rest of the world isn't post-classical. my guess is that yours was a building queue issue, but i don't know for sure. i hope you figure it out and that you have fun!