The magic_quotes_gpc PHP INI directive must be set to 'OFF' in order for OWA domstreams to operate correctly.
How do you make this change in Plesk server 9.5.4?
There would be several options:
Alternatively you can upgrade to Plesk 10.4 or Plesk 11.0 and manage PHP settings from UI. It will also ensure your securiyt as older versions of Plesk were a subject of vulnerability recently.