Every plugin install/update reports ERROR

Every time I install a plugin using the WPMUDEV dashboard, the download label turns to a red ERROR. Also when I download or update any plugin via WP, it goes off to do the install/update, but the cursor never comes back. In both cases, if I wait and refresh the page, the install/update has been successful, its just that there seems to be a disconnect in the signalling.

Any idea what can be causing it and how I can resolve the problem?

Terence.