Google Docs has an annoying redirect bug that is vexing users.
The bug apparently occurs when a user has both a Gmail account and a Google Apps account. The cookies get confused and then you're in redirect hell.
The fix for now appears to be to use your Gmail and Google Apps accounts in different browsers. That has been my fix since I also have Gmail and Google Apps and the two sometimes conflict.
In any case, this redirect bug has become the top issue on Google's known issue page for Docs. A few searches indicate that this bug is long-in-the-tooth.