Why won't my Minecraft Server GUI open?

Well, it was working before and I don't know what happened but when I loo in the logs this is what it says
[18:59:45] [main/FATAL]: Failed to start the minecraft server
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:… ~[minecraft_server.1.7.9.exe:?]
at com.google.gson.Gson.fromJson(Gson.java:… ~[minecraft_server.1.7.9.exe:?]
at nr.b(SourceFile:156) ~[minecraft_server.1.7.9.exe:?]
at nr.(SourceFile:42) ~[minecraft_server.1.7.9.exe:?]
at net.minecraft.server.MinecraftServer.
at ls.(SourceFile:53) ~[minecraft_server.1.7.9.exe:?]
at net.minecraft.server.MinecraftServer.mai… [minecraft_server.1.7.9.exe:?]
Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1
at com.google.gson.stream.JsonReader.beginA… ~[minecraft_server.1.7.9.exe:?]
at com.google.gson.internal.bind.Collection… ~[minecraft_server.1.7.9.exe:?]
at com.google.gson.internal.bind.Collection… ~[minecraft_server.1.7.9.exe:?]
at com.google.gson.Gson.fromJson(Gson.java:… ~[minecraft_server.1.7.9.exe:?]
… 6 more
When i click on the.exe file it loads but doesn't open