[Deceptor]

Mental - I see no replication of this myself, if you disable vB Optimise does this problem go away? The ACP isn't something we directly hook into.

vidan - Seems a function which is part of a blank failsafe is triggering the error as items returned are not srrings (although they should be). Try editing the class_activecache.php file, find this:

if (trim($item) == '{_______VB_ACTIVE_CACHE_BLANK_______}')

Replace with:

if (@trim($item) == '{_______VB_ACTIVE_CACHE_BLANK_______}')

Save and upload, this should hide the error, after which I'd suggest you ensure vB Optimise is successfully caching and pulling data from cache.

Red-Devil - The WOL cache can be a little tipsy, something that needs to be reviewed