Khaikok, Techlover is right here. Its pretty common. it's probably not a "refusal" when they are asking for more information. the more important thing to do is to understand WHAT precise they want and WHY they want it. Once you know the answers to these two questions, just make sure that they give them what they need. some of the common documents that are asked of applicants are updated form I-864, an expired police report submitted earlier etc. at this stage, it is NOT very likely that there are serious problems with the issue.

I am an attorney but please do not take the above as legal advise rather a general information.