I am trying to get an existing EE site working with MSM. I upgraded the site earlier from 2.1.2 to 2.9.3. Once that was working, I then installed MSM 2.1.7. When I enable MSM in the CP I get several PHP errors:

Message: apc_delete_file() [function.apc-delete-file]: Could not stat file /nfs/c10/h04/mnt/123456/domains/domain.com/html/system/expressionengine/config/config.php, unable to delete from cache. Filename: core/EE_Config.php Line Number: 1222

Message: Cannot modify header information - headers already sent by (output started at /nfs/c10/h04/mnt/123456/domains/domain.com/html/system/codeigniter/system/core/Exceptions.php:170) Filename: core/EE_Input.php Line Number: 213

Message: Cannot modify header information - headers already sent by (output started at /nfs/c10/h04/mnt/123456/domains/domain.com/html/system/codeigniter/system/core/Exceptions.php:170) Filename: libraries/Functions.php Line Number: 446

Once this happens, trying to access any page on the site gives "Site Error: Unable to Load Site Preferences; No Preferences Found" messages. Disabling MSM in the config.php gets the site working again, but how do I complete this so that MSM is working?

2 Answers 2


The first message would kind of cause the following 2. The first error also implicates APC (Advanced PHP Cache).

I would disable APC for the time being to see if you can bring the MSM site back up. If this works then I would guess there's some sort of EE Config / Cache conflict.

I couldn't hazard an exact resolution as I haven't worked with MSM for quite an while, and while I have used APC and MSM, never together (a quick search for MSM & APC doesn't yield much). But I hope this at least helps you test and narrow down the issue!

Also, MSM is an EllisLabs product, perhaps they'll give you a bit of support on this?

  • I do not know if I can disable APC because this is on a shared hosting server, but I will investigate that. Thanks! Commented Apr 21, 2015 at 15:21
  • For testing, I do beleive you can turn APC on or off via htaccess by setting a definition somewhere, worth a punt :) Keep the question history fresh and let us know how you get on!
    – Blatant
    Commented Apr 21, 2015 at 15:54

It turns out that there was a bug in EE. It took several weeks to get it resolved, but this fixed it:


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