Stupid me.
We were on a time crunch for giving a demo. A friend wrote a piece of code and he said it was working exactly the way it should be and that we can directly transfer to my machine and run it. He ran the piece (on his machine to show me) and it worked.
I take the source from him transfer it on my machine (because mine was going to be used for the demo).
Demo begins, everything goes smoothly ...all up until the point of the last module demo. Alas, the transfered module didn't work. Tried debugging during the demo as everyone was cooperative and patient. Turns out I hadn't done an initial setup required for that module. Embarrassed! 😓
Should have tested before the demo. 😞
FML. But from that moment forward i make sure to test every code I get from others as well as the one I write.

For anyone planning to ask me, I don't remember what the piece of code even did. It was a small time side project with a company. Not revealing the company's name.