[Backup] fails when including resources

I am trying to run the BACKUP on a site including 'Database & Resources' but it fails to download the .zip file.

If I just select 'Database Only' it downloads fine.

When I look at the online files there is a .zip file of 130mb in the backup folder containing the Resources and Database. Why would this not download fully.

Safari says "Decompression Failed". If I trying Firefox I just get an error page.

Looking at my server log it says the following:

[01/Oct/2014:11:53:37 +0100] "GET /perch/core/inc/keepalive.php HTTP/1.1" 200 354 "https://www.website.co.uk/perch/addons/apps/perch_backup/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.77.4 (KHTML, like Gecko) Version/7.0.5 Safari/537.77.4"

Any suggestions?