Hi Ronny,
The PHP error is a bug, however the line it has invoked means your using eAccelerator and it's not configured correctly to allow flushing. The message should say:
vB Optimise: Your eAccelerator requires you to specify permission to this directory to allow vB Optimise to clear your cache. For more information please visit
http://bart.eaccelerator.net/doc/php...elerator_clear
Once that's resolved, the error shouldn't occur anymore.
I'll get the error patched in the next release regardless