Dev Tools & Code
If you ever come across issues with one particular machine not able to parse a double or compare a date or something along those lines, particularly if the primary user of that machine speaks a different native language, check the Regional and Language Options under Control Panel.
If they have their machine's format set to something other than English (United States) then some of your code (albeit poorly written code) may not work properly. This has happened to me a couple of different times in some older code that people still use at work where our data is stored as strings but we need to parse them into dates or doubles.
Here's an example of the different formats (US English compared to CA French):
