OSX 10.10.5 update can't be installed

I finally got around to updating to 10.10.5 and I get the message "OS X update can't be installed on this disk. This volume does not meet the requirements for this update" What does this mean? I thought it meant it there wasn't enough space on the hard drive but I currently have 366GB out of 498GB free.

I have a late 2011 macbook pro. I do not want to get el capitan at this point in time either.