Hi Valerie,
Out of curiosity can you please try taking a copy of the file and putting it somewhere else to see if you can open it from there? I.e. if it's on the desktop move to the c drive, or vice versa.
Have you tried everything in this article:
http://kb.reckon.com.au/issue_view.asp?ID=3626
Kind regards,
Sally McIntosh (Sally@samsolutions.com.au)
Has this issue just started happening today or for a while?
Do you have a recent backup you can restore?
Sally