Here's a quick fix if anyone gets the above problem..
Using your favourite FTP app.. (mine is filezilla)
1) Browse in the left panel and find an old 'plugins/woocommerce' directory from a recent backup (pre update to have the old version of the woocommerce plug-in in..)
2) FTP into your site, go to:
3) Delete the woocommerce directory - may take a mo..
4) Upload your old woocommerce directory into the plugins folder and..
Now you can log-in to your admin, go plug-ins and reactivate your woocommerce plug-in - Website back up!
If your current theme will not take the woocommerce update, then don't update!
Note, if you don't have an old copy of the woocommerce plugin folder, you can still delete the folder via FTP which will then at least allow you to log-in to your wordpress site, change the 'appearance/themes' to a compatible one and then add the new version directly from your site in the plugins/add new