There has been some issues with the new El Capitan build, mainly due to an update to the Mac App Store signing certificate, Apple has communicated the following:
Last week we updated the Mac App Store app signing certificate. This was a planned event and most users experienced no issues. However, some users experienced some issues during this change. We have corrected those issues, and wanted to share this update with you.
Unfortunately, a caching issue with the Mac App Store meant that some users had to restart their systems and re-authenticate with the Mac App Store to clear a system cache of some outdated certificate information. We are addressing this caching issue in an upcoming OS X update.
For most users, simply uninstalling and reinstalling should fix the issue, as well as hopefully the coming update.
Please let us know here or via [email protected] if you still experience an issue and our apologies for the current inconvenience. We're working hard to fix it.
Decked Builder Support