getting an error message upon launching the game

When I click "play" on the launcher, i get the following message: "[14:34:48] [Client thread/INFO]: Setting user: Roanski23 [14:34:48] [Client thread/INFO]: (Session ID is token:0711486542c448ddbb44dac90163e2b9:0d4c029ce5024306a82e83d0095184d4) Exception in thread "Client thread" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1 at com.google.gson.Gson.fromJson(Gson.java:815) at com.google.gson.Gson.fromJson(Gson.java:768) at lu.b(SourceFile:151) at lu.<init>(SourceFile:43) at net.minecraft.server.MinecraftServer.<init>(SourceFile:155) at bpp.<init>(SourceFile:41) at avf.<init>(SourceFile:291) at net.minecraft.client.main.Main.main(SourceFile:124) Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1 at com.google.gson.stream.JsonReader.beginArray(JsonReader.java:338) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:79) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:60) at com.google.gson.Gson.fromJson(Gson.java:803) ... 7 more Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release"