Missing website results

I have (or had) piwik working happily on several sites, with piwik itself hosted on one ‘master’ site.
I had 2 sites running piwik, and 3 others (including that ‘master’ site) which were created as websites, but on which I had not yet installed piwik.
As of a couple of days ago, the ‘active’ sites aren’t found on the reports, although I can still see them in the database. I can’t select them from the dropdown, they aren’t in the list of sites on the ‘Websites Management’ page and reports run with the correct idSite number give the master site instead. (The inactive sites are present, but of course has all ‘zeroed’ data)
Its very annoying style_emoticons/<#EMO_DIR#>/sad.gif
Can anyone advise on what to do to fix this? I was quite liking piwik!

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