When you press the PLAY button, the following is displayed and the game does not start.

Gameplay locked up (and machine was forced to restart) this morning and this has been happening ever since.

[16:52:52] [Client thread/INFO]: Setting user: frankandhersch
[16:52:52] [Client thread/INFO]: (Session ID is token:f40029f3daf4435b9237dca0628971c4:666f0b49560a4a76a0ba79217707c859)
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:293)
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