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that some users had to restart their systems and re-authenticate with the Mac App Store to clear a system cache of some outdated certificate information.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.
Rick
Decked Builder Support