The above responders sound like doomsday prophets. It could just be a clerical or technical problem. Generally, a denial will be preceeded by some sort of request for evidence or interview request. Please keep us posted about what happens. A denial for renewal does not necessarily mean you will be put into removal proceedings.
You will most likely need an attorney to assist you with your husband's green card denial. It probably has something to do with a violation of the "good moral character" requirement which usually means that they have discovered some kind of criminal activity or fraud in his record. It is most likely that he will next be put into deportation proceedings. An attorney will be able to help you explore options such as cancellation and restoration of his Legal Permanent Residence status if that is possible.
There are many reasons for denial. Criminal activity or not lifing in the US for at least 6 months a year can lead to a denial as well as failure to pay taxes. It is very likely that your husband will receive a letter in the mail called a Notice to appear before an immigration judge because he will be placed in deportatin(now called removal) proceedings. I strongly urge you to consult an attorney as the government will have an attorne to make the case against your husband.
Alexus Sham, Esq.