According to an Associated Press article dated March 2, 2007, a company (170 soldiers) of Swiss soldiers lost their way during a nighttime exercise and marched into neighboring Lichtenstein. Apparently, noone in Lichtenstein noticed the troops before they realized where they were and returned to Switzerland.

Here is one link to the article: http://www.newsday.com/news/nationworld/wire/sns-ap-mistaken-invasion,0,2907128.story?coll=sns-ap-nationworld-headlines