I'm experiencing the same issue on both Android and desktop using my new Google Apps account. I have no problem with the old standard gmail account, only the new one.

My Apps account is less than two weeks old. I thought at first the error 500 was happening because I was signed into both accounts; one on Android and one on desktop.. not so. I also tried clearing cache, still no luck.

I have no clue on what to do. (hey, that rhymes)