How do I check regional settings?
Simple way is to look at the clock on the desktop, the date there should be in the format of your regional settings. If one is day/month/year and the other is month/day/year then that will tell you that the regional settings are different.

You might be able to use a different formula that wouldn't fail if the regional settings are different, but we would need to see how the date is constructed in the existing formula before we would be able to advise on that.