Export 5.1.2 and Import Using 6.0.X

Hi,

I'm trying to restore a backup i have from TC 5.1.2

I'm restoring it using TC 6.0.X and i'm getting an exception:

>maintainDB restore -F D:\backup_file.zip -T D:\database.properties
TeamCity maintenance tool. Copyright 2010 JetBrains s.r.o. All Rights Reserved.

Command line arguments: restore -F D:\backup_file.zip -T D:\database.properties
Using TeamCity data directory: C:\.BuildServer
Restoring from backup file: D:\backup_file.zip
Starting restore
Opening zip file: D:\backup_file.zip
File (charset) not found in the archive.
java.io.FileNotFoundException: File (charset) not found in the archive.
        at jetbrains.buildServer.util.zip.FileZipReader.openBinaryFile(FileZipReader.java:100)
        at jetbrains.buildServer.util.zip.FileZipReader.openTextFile(FileZipReader.java:87)
        at jetbrains.buildServer.serverSide.maintenance.RestoreProcessor.readCharset(RestoreProcessor.java:151)
        at jetbrains.buildServer.serverSide.maintenance.RestoreProcessor.openZip(RestoreProcessor.java:143)
        at jetbrains.buildServer.serverSide.maintenance.RestoreProcessor.runProcess(RestoreProcessor.java:99)
        at jetbrains.buildServer.serverSide.maintenance.AbstractMaintenanceProcess.run(AbstractMaintenanceProcess.java:1
52)
        at java.lang.Thread.run(Thread.java:595)
Restoring finished with errors
Critical error has occurred during command execution.

Any idea? Thanks.