BuildAgent upgrade failed

Hi all,
i have problem starting an agent. It won't update and always roll-back, seems a problem with permissions but everyone as full control on folder buildAgent.
Seems that every time fail to unpack a different package.. don't know why the message is access is denied. (the agent is installed on the same machine as the server, winxp)
Wondering what can be. Any ideas?

Follows a piece of upgrade.log



C:\TeamCity\buildAgent\plugins\tfs-agent.zip
[2010-02-22 10:23:44,093]  DEBUG - buildServer.agent.LauncherUtil - Copy from C:\TeamCity\buildAgent\update\plugins\xml-report-plugin.zip to C:\TeamCity\buildAgent\plugins\xml-report-plugin.zip
[2010-02-22 10:23:44,093]   INFO - buildServer.agent.LauncherUtil - Unpacking C:\TeamCity\buildAgent\plugins\ant.jar: 3514421 bytes
[2010-02-22 10:23:44,125]  ERROR - ver.agent.upgrade.AgentUpgrade - Upgrade failed :C:\TeamCity\buildAgent\plugins\ant\KEYS (Access is denied)
java.io.FileNotFoundException: C:\TeamCity\buildAgent\plugins\ant\KEYS (Access is denied)
    at java.io.FileOutputStream.open(Native Method)
    at java.io.FileOutputStream.<init>(FileOutputStream.java:179)
    at java.io.FileOutputStream.<init>(FileOutputStream.java:131)
    at jetbrains.buildServer.agent.LauncherUtil.saveEntry(LauncherUtil.java:128)
    at jetbrains.buildServer.agent.LauncherUtil.unzip(LauncherUtil.java:105)
    at jetbrains.buildServer.agent.upgrade.UnzipUpgradeFolder.extractAll(UnzipUpgradeFolder.java:33)
    at jetbrains.buildServer.agent.upgrade.UnzipUpgradeFolder.doUpgrade(UnzipUpgradeFolder.java:25)
    at jetbrains.buildServer.agent.upgrade.UpgradeFolder.upgrade(UpgradeFolder.java:36)
    at jetbrains.buildServer.agent.upgrade.AgentUpgrade.doUpgrade(AgentUpgrade.java:83)
    at jetbrains.buildServer.agent.upgrade.AgentUpgrade.applyUpdates(AgentUpgrade.java:55)
    at jetbrains.buildServer.agent.upgrade.UpgradeRunBase.run(UpgradeRunBase.java:32)
    at jetbrains.buildServer.agent.upgrade.UpgradeMode$3.run(UpgradeMode.java:39)
    at jetbrains.buildServer.agent.upgrade.Upgrade2.main2(Upgrade2.java:33)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:585)
    at jetbrains.buildServer.agent.ClazzLoader.call(ClazzLoader.java:59)
    at jetbrains.buildServer.agent.ClazzLoader.callMain2(ClazzLoader.java:19)
    at jetbrains.buildServer.agent.upgrade.Upgrade.main(Upgrade.java:16)
[2010-02-22 10:23:44,125]   INFO - ver.agent.upgrade.AgentUpgrade - AGENT UPDATE FAILED, exiting ...
[2010-02-22 10:23:44,125]  ERROR - ver.agent.upgrade.AgentUpgrade - TRYING ROLLBACK
[2010-02-22 10:23:44,125]   INFO - ver.agent.upgrade.AgentUpgrade - ===> Rollback agent upgrade due to error
[2010-02-22 10:23:44,125]  DEBUG - er.agent.upgrade.UpgradeFolder - UpgradeFolder: SimpleUpgradeFolder [bin] --> rollback


Thanks in advance for help.

Alain