What is this other coin? Maybe it uses the same address format as SpreadCoin.

epic fail.
You need to contact C-CEX and ask them for private key corresponding to this address. Then you will need to import this key into your SpreadCoin wallet but I'm not sure if this will actually work.They are going to ask for 0.5 BTC to correct the problem.
I am following/mining another coin where someone has the same issue.