problem opening emailed Gnucash file

[Mark Mason]

Hello Gnucash - I am treasurer of a not for profit CASC Sailing Club in UK.  I am just completing a years use of Gnucash.  I want to email my years accounts to my auditor.  I am on a mac she is on a pc and has installed gnucash.

I have twice sent her my completed yr end account by email (not including any log files) and she has not been able to open the file.  File has the extension .gnucash.  I have opened it myself with-out problem. 

Could you say what the problem could be with that amount of info?  Would be very grateful for advice - many thanks  - Mark Mason