Why this error message when trying to login into Charles Schwab?: "Login is temporarily unavailable. Please try again later or call customer support."

You have to ask Charles Schwab.

Are you trying to log in to your account directly on the Charles Schwab web site, or are you trying to import information from Charles Schwab into TurboTax? Schwab might have shut down their TurboTax import files sometime after April 15.

Maybe Schwab is doing systems maintenance over the Holiday weekend?

their computers may be shut down for maintenance on 5/30 because the markets are closed.  try again tomorrow.