I copied one account file in keystore folder from one computer to another. Mist reconnized the new account but complains "wrong password" when I use it. Is there more than just copying a file to importing an account?
When copying an account from the keystore you will need the password the key's were encoded with. This is the password that was used when each respective account was created.
You must enter this password to import the key and there is no way to access it without it. If your wallet is unlocked on the origin system, but you cannot recover the password, you could transfer it to a new address you are aware the password of. It is however likely to be locked on the origin system and require the password to send a transaction.
Hope this helps and good luck resolving your situation.