Hi,
I tried to install the Arduino Create Agent on Mac OS X El Capitan in Japanese environment, but crushed. I hesitate to post the whole crush report here, so please let me know personally if needed. 
10.11.5（15F34）
MacBook Air (11-inch, Mid 2013)
1.7 GHz Intel Core i7
8 GB 1600 MHz DDR3
Google Chrome 50.0.2661.102 (64-bit)
Hi Shigeru,
please post everything which could help us debugging the issue, or if you prefer send me a PM with the stacktrace 
Thank you very much for reporting, internationalization/extended charset bugs are quite difficult to discover for us so your bugreport is really important
I just installed the Create Agent on El Capitaine and it worked fine.
Curious to see what went wrong with the other user ...
Create folk: contact me if you want to look around my configuration to see why mine worked and Shigeru's didn't.
Charlie in Houston (CyberchuckTX)
Tying to install agent on El Capitaine here.... completes, but Problem running post-install step.... Erroe running security add-trusted-cert....
I could not complete the install either.
Poked around in the installer.
If I interactively ran the executable..
[ ArduinoCreateAgent-1.1-osx-installer.app/Contents/MacOS/osx-intel ]
it throws an error, both on the command line and in the gui.
MacPro # ./osx-intel
dyld: Symbol not found: _objc_release
Referenced from: /Users/bruce/Applications/ArduinoCreateAgent/ArduinoCreateAgent.app/Contents/MacOS/Arduino_Create_Bridge
Expected in: /usr/lib/libobjc.A.dylib
Checked the directory that the installer was looking [ ca.cert.pem ] and it is missing. Is the installer supposed to generate it?
MacPro # pwd
/Volumes/arduino-create-agent 1/ArduinoCreateAgent-1.1-osx-installer.app/Contents/MacOS
MacPro # ls -l
total 1198
-rwxrwxrwx 1 bferjul symapi 388 May 23 12:03 installbuilder.sh
-rwxrwxrwx 1 bferjul symapi 1222784 May 23 12:03 osx-intel
impossible to launch installer (issue with the dmg too but force extraction) with these errors in the console :
05/06/2016 23:44:09,302 com.apple.xpc.launchd[1]: (com.bitrock.appinstaller.626592[4281]) Could not find and/or execute program specified by service: 13: Permission denied: /Users/xxxx/Downloads/ArduinoCreateAgent-1.1-osx-installer/ArduinoCreateAgent-1.1-osx-installer.app/Contents/MacOS/installbuilder.sh
05/06/2016 23:44:09,301 Finder[437]: spawn_via_launchd() failed, errno=111 label=com.bitrock.appinstaller.626592 path=/Users/xxxx/Downloads/ArduinoCreateAgent-1.1-osx-installer/ArduinoCreateAgent-1.1-osx-installer.app/Contents/MacOS/installbuilder.sh flags=1 : LaunchApplicationClient.cp #1136 LaunchApplicationViaLaunchDJobLabel() q=com.apple.root.default-qos
05/06/2016 23:44:09,301 Finder[437]: spawn_via_launchd() failed, errno=111 label=com.bitrock.appinstaller.626592 path=/Users/xxxx/Downloads/ArduinoCreateAgent-1.1-osx-installer/ArduinoCreateAgent-1.1-osx-installer.app/Contents/MacOS/installbuilder.sh flags=1
05/06/2016 23:44:09,305 com.apple.xpc.launchd[1]: (com.bitrock.appinstaller.626592[4281]) Service setup event to handle failure and will not launch until it fires.
SIP partialy disabled to use xtrafinder
Hi Any updates on this issue? Are you still having trouble with it? We have been testing carefully on our Mac machines and unfortunately we are not able to reproduce it. Keep us posted!
This appears to be an issue caused by not being able to update the Trust Certificates. May be caused by Enterprise software, or not having admin privileges.
I experienced the same issue. I resolved by opening Keychain Access and finding the Arduino Certificate (which had a red x icon next to it). Open this cert and click Trust Always.
Restart the ArduinoCreate Agent, and then I could connect and upload!
@benzqn great news, thanks for finding this out. Are you in an enterprise environment? Are you admin of your Mac?