It's probably due to a poor crack, the reason you can take glass out of the GUI is because an error would've been thrown therefore stopping any sort of event handlers cancelling the GUI interactions. If you can link me the plugin I may be able to fix it (the uncracked version).
Try putting -noverify earlier in the command, for example (from your pastebin): java -Xmx10G -noverify -jar spigot18.jar
EDIT: I completely had forggoten that putting anything after -jar <jarfile> adds it as an argument
Name: Koupah
How I found BlackSpigot: When searching for plugins at some point 2 years ago because I wasn't keen on shilling money for minecraft stuff
About Me: 18, Like to develop software and interested in cracking programs
Other: I'm wondering how many posts you need before you can download...