HTTP Status 503 - Servlet NewFrontend is currently unavailable
Type: Status report
Message: Servlet NewFrontend is currently unavailable
Description: The requested service (Servlet NewFrontend is currently unavailable) is not currently available.
The solution is the same as previously - Clear your Blogger cookie.
At any time, the individual Blogger server, thru which you are accessing your blog, may become extremely busy, or may go off line for some, unexplained, reason. This is an unfortunate reality in the server world.
By clearing your Blogger cookies, you can force Blogger to "randomly" assign you to another server. Sometimes, you may get the same server back; other times, you may be assigned to yet another broken server. So you might have to try clearing your Blogger cookies repeatedly.
If the problem is with a cluster of servers, or if you're reassigned the same server as before, you may continue to get the same error. Keep trying, until you are "randomly" assigned a working server.
Patience and persistence.