If I assume that you have not used the same credentials as before, could it be that your password is longer than 31 char?
Also try to avoid funny characters in SSID and password (non US keyboard layout).
Could you try if you can connect when you got your WiFi open (temporarily)?
Sorry forgot the link for the CLI installer in my previous post
Toolchain for Windows Installer
CLI would be really useful in this case.
Other stabs in the dark:
Have you wiped the old credentials off the Photon (SETUP 10+ sec till rapid blue)?
How does the device behave in Safe Mode?
Have you ever used WiFi.selectAntenna() in any of your programs?