Comment by rikroots

The very first time my company farmed me out to work onsite with a client. Day 1, Job 1: download the client's website code and get it running on my laptop.

... It just wouldn't work. Everything I tried - failed. Everything else on my laptop was working fine, except this code. Everyone else who had ever downloaded the code had managed to get it working on their machines within a couple of hours. Colleagues working onsite with me tried to help, but everything they tried - failed. Finally the decision was taken to reset my laptop to factory defaults and reinstall everything. That took up half of Day 2. Tried to get the client's site running - failed! Things were beginning to get really embarrassing - all this was happening in full view of the clients. In desperation, my company called me back to their offices and issued me with a new laptop. Back onsite, the code downloaded ... and worked first time!

Turned out that the issue was that my hard drive filesystem had been setup (not by me!) as case-sensitive, and the client code included a file with an all-caps filename, which the code called using a lowercase string. Almost lost my job over that one.