221(G) letter received on embassy appointment

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Hello, my brother had an interview on the Colombia embassy yesterday, He had been living in the US for 7 years as an F1 student, recently he found a company that sponsored him to get the H1-b Visa, so he got the approval here in the US. He decided to go to Colombia for Christmas, and so he apply for an appointment in the Colombia embassy to be done with his H1-B Visa. He went yesterday and the consul told him that he had to wait, so he gave him an 221(g) letter, saying that they had to do some things (No idea what kind of things) and that they would call him for a new interview. The letter says that please not to schedule another appointment, not to call USCIS, not too call the embassy... it says he just have to wait until they contact him... any idea what's going on behind this letter??? how long does it take??? an why, after he got the approval of his H1-B visa here into the US, and he was convinced there wasn't going to be any problem with the interview, he received this letter??? any other people with the same case??? I research and there are a lot of cases with "based-on-marriage" visas, but no so many with H1-B visas... please any help would be grateful, my brother is really sad because he is supposed to come back to work on January 5th, and probably this is going to take more than one month... Thanks, and please don't pay attention at my signature or timeline since that is my personal case base on marriage. THANKS!