Moderator Note
For some people, reinstalling fixes this issue. To do so, press your Windows+R keys, type in %AppData% at the dialog, and press Enter. In the window that appears, open the .minecraft directory, and delete everything except for the saves directory that you see therein. Then, try running Minecraft again.
[19:48:42] [Client thread/INFO]: Setting user: <username>
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 sa.b(SourceFile:148)
at sa.<init>(SourceFile:42)
at net.minecraft.server.MinecraftServer.<init>(SourceFile:154)
at cyk.<init>(SourceFile:40)
at bss.<init>(SourceFile:285)
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
Linked issues
is duplicated by 57
Attachments
Comments 19
Sorry Mustek, but it looks like this is an error in a JSON file somewhere, therefore an issue with the game (also note Exception in thread "Client thread"). Considering it gives an error right at startup, it's probably not a resource pack issue.

No, it's an actual issue which many people suffer from.
Reopened and redesigned.
will it delete my servers? it did delete them 😞
Having the same issues. I have tried uninstalling and reinstalling. Still receiving the same errors.
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
Reoccurred in 1.8.6, here's a screenshot
This issue is occurring on my MC 1.9 server.
I have tried deleting the usercache.json
Still does not work.
I fixed this issue on my 1.10 server by deleting all of the .json files. However, when I try to join, I get the same error as if the server was not up (java.net.ConnectException: Connection refused: no further information: ). However, the server seems to be running fine...
EDIT: When I checked server.properties, all the settings were reset/messed up. I can join fine now.
Is this still an issue in the latest snapshot 16w44a? If so please update the affected versions.
This is an automated comment on any open or reopened issue with out-of-date affected versions.

Is this still a issue in the latest version of the game(currently 1.13.1)?
If so, please add it to the affected versions, thanks!
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