Interesting, thanks for the info !I suspect that the TS was trying to use their "grid square" as their location while XenForo is looking to parse a zip (or postal?) code.
"Grid square" is an alternative method of expressing an Earth-bound location versus zip code or latitude and longitude. Grid square is typically more precise than zip code but a little less precise than latitude and longitude. The theory goes that your grid square is much easier to memorize and recite than your latitude and longitude.