Minecraft server errors

This error:

java.io.FileNotFoundException: ./world/poi/r.0.0.mca (Permission denied)
at java.io.RandomAccessFile.open0(Native Method) ~[?:?]
at java.io.RandomAccessFile.open(Unknown Source) ~[?:?]
at java.io.RandomAccessFile.<init>(Unknown Source) ~[?:?]
at java.io.RandomAccessFile.<init>(Unknown Source) ~[?:?]
at byd.<init>(SourceFile:99) ~[server.jar:?]
at bye.a(SourceFile:40) ~[server.jar:?]
at bye.a(SourceFile:58) ~[server.jar:?]
at byf.d(SourceFile:146) [server.jar:?]
at byf.a(SourceFile:58) [server.jar:?]
at aqk.a(SourceFile:153) [server.jar:?]
at uu.a(SourceFile:382) [server.jar:?]
at vg.a(SourceFile:298) [server.jar:?]
at vi.a(SourceFile:310) [server.jar:?]
at net.minecraft.server.MinecraftServer.b(SourceFile:824) [server.jar:?]
at ui.b(SourceFile:343) [server.jar:?]
at net.minecraft.server.MinecraftServer.a(SourceFile:763) [server.jar:?]
at net.minecraft.server.MinecraftServer.run(SourceFile:631) [server.jar:?]
at java.lang.Thread.run(Unknown Source) [?:?]
[14:04:30 ERROR]: Error writing data to disk

and ones like it show many many many many times