[Plugin: Flickr Photo Post] serves up garbled code

I have a wierd anomaly going on and I have no idea how to solve it.

On two separate domains (hosted on different servers), each running WP 3.3.1 with a raft of plugins, on one install Flickr Photo Post works perfectly and on the other I get junk like the following:

{"page":1,"pages":6745,"perpage":6,"total":"40470","photo":[{"id":"104425830","owner":"89273442@N00","secret":"063545037b","server":"41","farm":1,"title":"Tank","ispublic":1,"isfriend":0,"isfamily":0},{"id":"2727110892","owner":"12068800@N00","secret":"35494f1ea4","server":"3139","farm":4,"title":"Water tank","ispublic":1,"isfriend":0,"isfamily":0},{"id":"2489626460","owner":"13977398@N03","secret":"2f3c72e0b8","server":"3194","farm":4,"title":"Canadian tank","ispublic":1,"isfriend":0,"isfamily":0},{"id":"1278518191","owner":"37804979@N00","secret":"6b7be6e9c8","server":"1019","farm":2,"title":"Tank","ispublic":1,"isfriend":0,"isfamily":0},{"id":"2157028713","owner":"64937321@N00","secret":"024975f832","server":"2232","farm":3,"title":"My iPond 'torture tank' at Work.","ispublic":1,"isfriend":0,"isfamily":0},{"id":"4590063376","owner":"50059357@N08","secret":"158f6a96ca","server":"4039","farm":5,"title":"tank","ispublic":1,"isfriend":0,"isfamily":0}],"search":"tank"}
`
I really want to be able to use this plugin. Anyone got any ideas what’s going on?
Are there known plugins that do not work alongside Flickr Photo Post.

Most of my other plugins are up to date.

Thanks for any pointers.

http://ww.wp.xz.cn/extend/plugins/flickr-photo-post/