Key.ppk Error when Opening WinSCP Console

I get the following error when I try to open WinSCP console.

C:\Documents and Settings\x1030\Desktop\FileZilla-3.5.1\key.ppk does not exist or it does not contain private key in known format

It was working up to a couple of days ago. Can anybody help?

Regards,

Peter.

Does the file exist? Is it accessible to WinSCP process?