Like last Patch Tuesday, and many Patch Tuesdays before it, this Patch Tuesday SharePoint 2013 was blessed with an update, the April 2015 CU. There are a few outstanding Regressions from previous SharePoint 2013 CUs, so folks jumped on it pretty quickly.
Turns out the April 2015 CU has a dark side.
A year ago, when SP1 came out, it had some problems. I cover them in my blog post “Don’t Install SharePoint 2013 Service Pack 1” The original version of SP1 had this nasty bug where it prevented the installation of subsequent patches. That’s a bad thing. Microsoft cleaned everything up and rereleased SP1 without that issue. They also advised that if you were an MSDN or Volume License customer, the SharePoint 2013 installation ISO that included Service Pack 1 was not affected by that. Whew! It was still a bit confusing, as the Bad SP1 and the Good SP1 looked the same to a SharePoint administrator trying to fix the problem. I talk about how to tell them apart in this blog post, “How to tell which Service Pack 1 you have installed on SharePoint 2013” I thought that was the end of the story.
Turns out I was wrong.
The April 2015 CU is the first SharePoint 2013 CU that requires Service Pack 1 be installed. The previous CUs required either Service Pack 1 or the March 2013 CU. If the installer found either of those installed, it continued on. With the April 2015 CU only Service Pack 1 could scratch that itch. And the different versions of Service Pack 1 leave different footprints on your SharePoint farm. One scratches the April 2015 CU itch, one does not.
If you installed your SharePoint farm with the ISO media that included Service Pack 1, you will not be able to install the April 2015 CU. The April 2015 CU does not recognize that the required bits are in place and its installation will fail. Fortunately, there is a workaround. If you reinstall the stand alone Service Pack 1 (download links here) you’ll then be able to install the April 2015 CU. This is the fix even if you’re running a post Service Pack 1 CU. So if you’re currently sitting at the November 2014 CU and you want to install the April 2015 CU, you have to reinstall Service Pack 1 first. Obviously, right? 
One tricky aspect of this is language packs. They have the same issue. And since CUs also patch the language packs, a language pack can cause the April 2015 CU to break as well. For instance, if you installed English SharePoint 2013 (wonky ISO or not), put Service Pack 1 on it, then installed the German Language Pack that came with Service Pack 1, the April 2015 CU won’t install. Not because the base SharePoint (in this case English) doesn’t have the correct Service Pack 1, or even because the CU hates German, but because the Language Pack (German) doesn’t have the correct Service Pack 1. In this case the fix is to reinstall (or repair) Service Pack 1 for the Language Pack, then take another swing at the April 2015 CU.
Hopefully this has helped. I want to give shouts out to Stefan Goßner, Trevor Seward, and Brian Lalancette. We had a good discussion on Twitter about this this morning that helped flesh out the details.
tk
ShortURL: http://www.toddklindt.com/Apr2015CUNoBueno