????然而,，盡管受到旅客的熱情追捧,，但人們也一直對全球通關(guān)計劃有抱怨,，這些聲音——如果只能算微弱的話——是來自少部分在掃描指紋時遇到困難的會員,。當(dāng)那種事情發(fā)生時,，無人值守亭會顯示出一個“X”。這個信號會讓該名會員進入任意普通的入境安檢通道（或者在某些情況下是進入一條特殊的全球通關(guān)計劃問題通道）,。 但他或她必須像其他人一樣接受安檢人員的檢查,，而不是直接通關(guān)。

????瑪西亞?多恩是伊利諾伊州羅克艾蘭一家貨運公司的副總裁,，她在六個月前成為全球通關(guān)計劃的會員,，有一次她的指紋無法被掃描，導(dǎo)致她卡在一條入境通道中——她試圖插隊,，但無法通過——這讓她差點錯過飛往哥斯達黎加的轉(zhuǎn)接班機,。雖然多恩總的來說還是喜歡這項計劃的，但在那個時候她有了別的想法：“我花了100美元就得到這個,？”

????這個問題在TripAdvisor和FlyerTalk這樣的旅行網(wǎng)站上一直是討論話題,，并成為《紐約時報》商務(wù)旅行專欄作家喬?夏基的寫作素材，他對于全球通關(guān)計劃另一方面的“熱情”評論包含了這樣一則軼事，一位旅客無法完成指紋掃描,，直到他在海關(guān)工作人員出汗的額頭上把自己的手指按濕（說點近的,，《財富》雜志主編蘇安迪在申請加入全球通關(guān)計劃時也遇到無法讓掃描器讀取其指紋的問題）。

????這是怎么回事,？

????專家估計,，1-4%的人指紋太過模糊，無法被機器讀取,。有一些特定的群體更有可能遇到這方面的麻煩：跟化學(xué)品打交道的人,，或是從事多年手工勞作的人，抑或是皮膚干燥和患有皮炎的人,。

????這使得機場在讀取人們指紋方面頗具挑戰(zhàn)性,，因為乘客剛從飛行數(shù)小時的國際班機上下來，此前他們一直坐在空氣濕度只有5%的機艙內(nèi)（出汗額頭的作用就在這里）,。

????然而,，出問題的并不總是模糊的指紋。掃描器必須以正確的方式按壓,，手指需要平放在正確的位置,，并使用特定的壓力。掃描器不干凈時也會出現(xiàn)問題——據(jù)瓦格納稱,，工作人員每天都會對掃描器進行清理,，方法是用一截膠帶粘走掃描板上的污漬。在無人值守亭報出“X”之前,，每個人都有兩次機會讓機器正確讀取指紋,，否則他或她就得去見入境檢查員了。

????Yet for all the enthusiasm, the program has been dogged by complaints from a vocal if tiny minority of members who have had trouble getting the scanners to read their prints. When this happens, the kiosk prints out an X. That printout allows the individual to cut any normal immigration line (or in some cases go to a special Global Entry problem line). But he or she must still be cleared by an agent like everyone else, rather than cruising straight through immigration altogether.

????Marcia Dohrn, a VP at a trucking company in Rock Island, Ill. who has been enrolled in Global Entry for the past six months, nearly missed her connecting flight to Costa Rica when she got stuck in an immigration line -- she cut the line, but it didn't move -- after her prints wouldn't scan. Though she generally likes the program, the moment gave her pause: "I paid $100 for this?"

????The issue has been a topic of discussion at travel sites like TripAdvisor and FlyerTalk and fodder for New York Times business travel columnist Joe Sharkey, whose otherwise glowing review of Global Entry included an anecdote of failing the fingerprint scan until he wet his fingers on the sweaty forehead of the customs agent. (Closer to home, Fortune editor Andy Serwer also had problems getting the scanner to register his fingerprints when applying to the Global Entry program.)

????What's going on?

????Experts estimate that 1 to 4% of the population have fingerprints that are too faint to be read by machines. There are certain groups that are more likely to have trouble: those who have worked with chemicals or done years of manual labor, or people who have dry skin or dermatitis.

????That makes the airport, where passengers debark from hours of international jet travel -- seated in a cabin where air humidity is as low as 5% -- an especially challenging environment for reading fingerprints. (Hence the utility of the sweaty forehead.)

????Yet it's not always faint fingerprints that are the problem. The machines must be pressed just so, with fingers laid flat in the correct position and applying a particular amount of pressure. Issues also arise when the scanners are not cleaned -- a procedure that is done daily by laying a piece of sticky tape on the scanning plate, according to Wagner. At kiosks, individuals get two chances to get it right before they get an X and are sent to the immigration officer.