hey guys,
I suddenly have the same issue. If I go to plugin page. I get this “no valid header” message. Then all plugins are gone. I checked and saw that there is php 5.2 on the server. Could this be related to some hidden security updates in the past? I will now try to upgrade to 5.4 and give you an update.
If you solved a same issue, please feel free to tell me.
Regards,
quix