This was the answer from bter.com:
Please try to send it to the account, not theaccount key.
For example, if you have a registered account lily with the key 123455.
Please try to send asset to lily rather than the account key 12345.
When you are trying to send BTS to bter, please also send to the account btercom instead of BTSX567mPAbaXvB932Ky2c7tNkswP92dyFDkf8s2cfRFbzC2VfgMzf
This sounds strange, but it works!
No idea why the public key for transfers from bter.com to bitshares.org does not work ...