White screen of death

Long story short: a client came to me with a damaged/hacked D5 site and asked me to restore whatever possible.

On my local-dev I installed D7 with feeds and feeds_sql and tried to gather data from the old sql database.
I have a simple query: SELECT nid,title,timestamp FROM node_revisions WHERE uid > 0 LIMIT 5
But whenever I press save in the SQL Parser Settings I get a WSOD. Nothing gets saved to the error log so I'm having a quite a trouble hunting it down.

Queries are running just fine against the default DB. The only fail against the old DB.
The db declaration is like this:

 'old' =>  
  array (
    'default' =>  
    array (
      'database' => 'smartdogs',
      'username' => 'smartdogs',
      'password' => 'smartdogs',
      'host' => 'localhost',
      'port' => '', 
      'driver' => 'mysql',
      'prefix' => '', 
    ),  
  ), 

I've tried both mysql and mysqli drivers, with no luck.

Any ideas what might be producing the WSOD?

Thanks ;)