.xhb' is not a valid homebank file

I run Windows 8.1 and had Homebank 4.4 - During a critical upload today (when I was working on Homebank - but after I thought I had pressed Save) my computer crashed and I needed to reboot with Homebank still open.

I now get told that the designated "....xhb' is not a valid homebank file". I have years of data on this (some of it quite important).

I have rolled the operating system back to before the critical update - same message.
I have downloaded Home bank 5.0 but get the same message.
I have found the hidden back up and got the same message.

What else can I do? Ideally I want to use the file in Homebank. As a fallback just getting a 'read only' extract of the data will be OK.

Can someone please help.