I can't say what is wrong with your current openid, however, let's just get it fixed, eh? I suggest you pick a second OpenID provider - google might make sense, since you can use either gmail or your google profile. Create a second account on SO, and let me know which. In parallel, I'll e-mail the e-mail address on your original account; reply to confirm that it is you, and I'll merge the two accounts (you can have 2 OpenID records per account).
Then when (if?) your OpenID works again you can change back easily.
For info, the reason I ask you to create a second SO account is that gmail OpenID is not preditable.