The site appears to be down altogether.
“Dear Valued Customer,
We are currently experiencing some technical difficulties on singaporeair.com, and are working to rectify the problem. The website will be down from 1am to 1:30am Singapore Time (5pm to 5:30pm GMT).
You may wish to contact your local Singapore Airlines office should you require urgent assistance.
Your understanding is much appreciated, and we apologize for any inconvenience caused.