But when I start ./clam-qt I get this error: error initializing wallet database enviroment /home/username/.clam!
Do you have an existing wallet.dat in that folder, created using an incompatible version of the Berkeley DB? That's what it looks like to me.
Try renaming wallet.dat and trying again. It should make a new one. Use your old client to move any coins from the old wallet to an address in the new one.