Bukkit

Info:
Bukkit version: 1.5.1-R0.2 (Build #02754)
qQuests version: qQuests #2013

1. Server works with 0 players at night, qQuests "persisted to disk." every 5 minutes
2. Randomly, in one moment server crashes with error:
________________________________________________
2013-04-19 00:48:55 [SEVERE] null
java.io.IOException: Input/output error
at java.io.FileInputStream.readBytes(Native Method)
at java.io.FileInputStream.read(Unknown Source)
at java.io.BufferedInputStream.fill(Unknown Source)
at java.io.BufferedInputStream.read(Unknown Source)
at java.io.FilterInputStream.read(Unknown Source)
at org.bukkit.craftbukkit.libs.jline.console.ConsoleReader$1.read(ConsoleReader.java:167)
at org.bukkit.craftbukkit.libs.jline.internal.InputStreamReader.read(InputStreamReader.java:267)
at org.bukkit.craftbukkit.libs.jline.internal.InputStreamReader.read(InputStreamReader.java:204)
at org.bukkit.craftbukkit.libs.jline.console.ConsoleReader.readCharacter(ConsoleReader.java:995)
at org.bukkit.craftbukkit.libs.jline.console.ConsoleReader.readLine(ConsoleReader.java:1167)
at net.minecraft.server.v1_5_R2.ThreadCommandReader.run(ThreadCommandReader.java:31)
________________________________________________

Why I think that qQuest causes error? Because it persisted to disk every 5 minutes, and server crashes exactly after 5 minutes after qQuests save files last time.
_____________________________________________________
2013-04-19 00:24:49 [INFO] [qQuests] Quests persisted to disk.
2013-04-19 00:29:49 [INFO] [qQuests] Quests persisted to disk.
2013-04-19 00:34:49 [INFO] [qQuests] Quests persisted to disk.
2013-04-19 00:39:49 [INFO] [qQuests] Quests persisted to disk.
2013-04-19 00:44:49 [INFO] [qQuests] Quests persisted to disk.
2013-04-19 00:48:55 [SEVERE] null
java.io.IOException: Input/output error
_____________________________________________________

Maybe it's not qQuest fault, but I thought I must report about it. Thanks