Snapshot plugin - broke!

Hi folks,

There I was with my shiny WP site, it suggested that I upgrade to WP V3.5, but being the responsible type, I thought I'd better back up just in case there was a problem.

So I downloaded Snapshot, uploaded via my WP dash, hit "activate" and boom! .. wp-admin is now broken:

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Server error
The website encountered an error while retrieving http://travellercounselling.ie/wp-admin/. It may be down for maintenance or configured incorrectly.
Here are some suggestions:
Reload this webpage later.
HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfill the request.
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Any suggestions? Should I delete the snapshot folder via FTP?

Many thanks,

Richard