If your wallet was exported a json format backup file (.json) on 0.5.X version , and you try to import it in 0.6.1 or 0.6.2 , it won't work even if you input the correct password .
(backup the current wallet before the instruction below , in case something goes wrong )
You need to download 0.5.3 version wallet software , install it , then import the backup file , exit the wallet from file menu .
Then , you can re-install the 0.6.2 version wallet , now you would be able to use your wallet and the account in it .
And you can backup the wallet again by exporting an json file of this new version , it won't have the same issue next time .
This issue has reported by several users before , maybe there is a thread somewhere mentioned this solution , but some people couldn't find it .