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Backup the content of the database, fails to create a file

I am using Spip 2.1.26
Every month I backup the database to create the .xml.gz file
At the end of last month when i try to create the backup the web page says waiting for site.
It will do this for over an hour - If you refresh the page the page just reloads there are no error messages.

I would appreciate any help to get the backup working again.
Many thanks in advance,