After recently applying the July 2015 SharePoint 2013 Cumulative update we discovered that Infopath forms or pages referring them had stopped loading throwing a generic “something went wrong” error to the screen with a correlation id. After taking a look into the logs we found the following against the Infopath form services requests:
Requested registry access is not allowed
This appears to be a known issue within previous SharePoint cumulative updates (previously documented in the March cumulative update). There’s good writeups about this issue on Todd Klint’s always useful blog and on the accepted answer to this MSDN question. The problem appears to be the same in the July 2015 update – SharePoint updates the registry removing permissions for service accounts causing problems with Infopath and other areas (in our particular case BDS stopped working as well).
To resolve the issue you need to re-grant permissions for the user WSS_WPG to the registry group HKLM/Software/Office Server/15.0. After doing this power cycle the server and everything will function as expected again.