Sometimes the United States Citizenship and Immigration Services (USCIS) will make a determination that it needs more information before it can proceed with an application. This will prompt the USCIS to send a Request For Evidence (RFE), that will ask for specific information about issues that it feels needs more clarification and/or evidence, and will provide a deadline as to when the additional information needs to be presented.
Receiving a Request For Evidence (RFE) is not unusual, and it does not mean that the USCIS doubts your situation and/or will deny you the relief you are seeking. In fact, there are many instances where the USCIS will deny a petition without seeking more information.
The failure to respond to a Request For Evidence may lead the USCIS to believe that you are not interested in proceeding further and will issue a denial, or it may make a decision concerning your file based upon the information in it possession (which in most cases will mean a denial).