A few days now, I don't see it work when I click on an inventory (but it work fine when I use /fastcraft craft). I tried to add permissions but it still doesn't work :(
Note: I use the newest version on Spigot 1.9.4 server.

Hi. Can you run the command "/fcadmin debug" and copy the output here? It will help me figure out what might be causing the problem.

Okay, here's the output: http://pastebin.com/EWhhQ1qT

Have you tried toggling FastCraft+ with this command?
/fc toggle

I tried but it didn't work and I also found that: FastCraft+ interface show up, then back to the default interface, probably due to the plugin?

That's interesting. If you copy your server, and remove all plugins except for FastCraft+ and your permissions plugin, are you able to view the interface? It's possible that there's some interference with another plugin.

I feel this error very confusing :(
I disabled the AquaWarp plugin and FastCraft+ worked in my server.
then I created a new server, only include it and FastCraft +, it still works (troll?)

I solved that problem successfully by creating and using a new plugin called FixFastCraftPlus. It will run the command /fc craft when player left-clicks on a workbench and has permission.
https://mega.nz/#!GAFGDKwB!zGV7jnBvQ41PeQTYJlqhvtgtOQXryHzrDQNPa00QINA

Thanks for helping me and I hope you can create more great plugins! :)

This is definitely just a temporary workaround. I'll see if there is any conflict with AquaWarp, and what might be causing the interface to not open.

AquaWarp is cancelling all interaction other than left clicking blocks. This line.

Hmm. I will fix it.

you can see the source at https://github.com/anhcraft/AquaWarp/blob/master/vn/anhcraft/aquawarp/GUI/WarpGUI.java
and https://github.com/anhcraft/AquaWarp/blob/master/vn/anhcraft/aquawarp/Listeners/ClickWarpGUI.java