The old management portal is working fine for me. Earlier there was no management certificate under my subscription, so it was not showing anything. Later, I tried uploading a .cer certificate and it got uploaded successfully.
I hope it helps!! If you found this post useful, Please "Mark as Answer" or "Vote as Helpful". Thanks! Vaibhav Gujral.
In the preview Portal you can only manager Certificates for single "cloud services". In case you want to play with powershell or csupload .... stuff to manage windows azure you need to switch back to the "old" azure management portal to upload certificate.