This is odd .. the "import backup" should prompt for a dialog where you can simply select the file .. strange

it's done,i just put back the  .json file in Program Files>BitSharesX>bin.and everything is fine now,thank you for your help.

From in the client go to File-> import wallet. Then navigate to wherever your backup json is

do i need to put back the .json file in Program Files>BitSharesX>bin ?

It's a file not found error. Are you sure you're giving the right path?

i have check the backup file using text editor and there is no extra comma at the end of the file

i use Export Wallet to backup my wallet,but when i use Import Wallet to restore my wallet,it shows me a error:file not found(20019)