Error message when trying to "Configure Script Deferring"

Hello, I am getting an error message when I try to click the button to Configure Script Deferring on the Hummingbird plugin Performance Report page. Please see screenshots below:
Button page:
After pressing the button:

I thought this was caused by Adminimize plugin but I reset it to default values and then deactivated and the issue persists.

Please let me know if there's something I have probably installed or set that could be causing this.
Note: My web host has PHP Version 5.2.17

Regards,

Georgi