I installed APC as recommended and it seems APC is causing my problems. Basically, if the caching is enabled, anytime you go into a page to edit it, it says you are already editing it (so if I am logged in as admin, the message says “admin is already editing this page” and we can’t edit until we hard-refresh the page sometimes as many as 7 or 8 times). If we turn caching off, the sites are dreadfully slow, to the point that some time out before loading. Not sure if it makes a difference, but these are some of our larger content and feature heavy sites ( few add ons, etc). I’ve been experimenting with the ‘apc filter’ (a configuration parameter of APC) to force APC not to cache certain concrete5 php files. This helped at first but I think we need to know specifically which concrete5 php files are used in the backend (and add them to the apc filter). If we could find out which files should not be cached that could resolve the issue. Also, there may be other APC configuration options that could resolve this, I’m not sure since I’ve only used it starting this week. There is little to no documentation on this issue in the concrete5 forums and we can’t be the only ones experiencing it. I’ve seen a couple concrete5 forums related to the issue but none have a resolution. By the way, APC is the recommended/enterprise standard for PHP, it will be built into PHP6. The next best (or could even be better) caching engine is MEMCACHE which I don’t much about and could be much more complicated to setup. Let me know if you have any more questions. We are using Concrete5 version 5.6.0.2.