Expansion Problems...

[Raist]

internal server error---often along the lines of service not available/not found or authentication failed.

Either something is hosed with SE's link to the payment processor, or the payment processor is having issues.

Edit:
Afterthought. Could be an SSL issue. That bug in the last round of Windows Updates that reset SSL settings might be biting people in the arse here as well. Open your internet options (inetcpl.cpl from the run/search box) and go to the Advanced tab, then scroll to the bottom of the list. If any of the SSL and TLS options are unchecked, check them and apply the changes. Close and reopen your browsers to make sure it picks up the changes.