Minecraft launcher says "Error! Unable to start game!" when I click play.

Unable to start game. Was able to launch game fine two days ago. Before I tried deleting my folder this error message came up, "java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:374) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:165) ... 42 more"