THanks Marco
I've fixed this
It is caused by the language browser plugin being uploaded twice!
The fix for any future problems anyone has is to ...
In phpMYadmin go to the table "datastore" and look there for the record named "pluginlist". Delete this record.
Then you can login to your board again.
Login into admin-cp, go to the plugin-manager, Delete the duplicate entry of the plugin, and click on "Save Active Status", to rebuild the entry in the datastore.
Marco's way may be a better option?
This is the error message in case anyone has the same problem and does a search
Fatal error: Cannot redeclare rk_getenvvar()
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