This really looks like build agent upgrade failure.
Could you please do the following:
- on your "Agents" page, is there possibly "outdated agent" mark for this Ubuntu build agent?
- Could you please attach results of the following commands:
ls -l /opt/tc-agent/lib
ls -l /opt/tc-agent/plugins

thanks!

Agent on agent list is NOT marked as outdated. From your original suggestion, I wiped out the installation directory and re-installed from scratch.

Here's the output your asked for....

root@ptbuild05:~# ls -l /opt/tc-agent/lib
total 17600
-rw-r--r-- 1 root root 45386 2006-12-18 10:38 activation.jar
-rw-r--r-- 1 root root 5245 2006-12-18 10:38 agentInstaller.jar
-rw-r--r-- 1 root root 33408 2006-12-18 10:38 agentInstaller-UI.jar
-rw-r--r-- 1 root root 4026 2006-12-18 10:38 annotations.jar
-rw-r--r-- 1 root root 94649 2006-12-18 10:38 buildServerAgent.jar
-rw-r--r-- 1 root root 80009 2006-12-18 10:38 buildServerCommon.jar
-rw-r--r-- 1 root root 9832 2006-12-18 10:38 buildServerCommonRuntime.jar
-rw-r--r-- 1 root root 43437 2006-12-18 10:38 buildServerMessages.jar
-rw-r--r-- 1 root root 25600 2006-12-18 10:38 buildServerRemoteServerProxy.jar
-rw-r--r-- 1 root root 9814 2006-12-18 10:38 buildServerRuntimeUtil.jar
-rw-r--r-- 1 root root 2927 2006-12-18 10:38 buildServerServerLogging.jar
-rw-r--r-- 1 root root 59247 2006-12-18 10:38 buildServerServerModel.jar
-rw-r--r-- 1 root root 14508 2006-12-18 10:38 buildServerXmlRpcWrapper.jar
-rw-r--r-- 1 root root 168760 2006-12-18 10:38 commons-beanutils-core.jar
-rw-r--r-- 1 root root 46725 2006-12-18 10:38 commons-codec-1.3.jar
-rw-r--r-- 1 root root 571259 2006-12-18 10:38 commons-collections-3.2.jar
-rw-r--r-- 1 root root 107631 2006-12-18 10:38 commons-dbcp-1.2.1.jar
-rw-r--r-- 1 root root 278799 2006-12-18 10:38 commons-httpclient-3.0-rc4.jar
-rw-r--r-- 1 root root 38015 2006-12-18 10:38 commons-logging.jar
-rw-r--r-- 1 root root 62103 2006-12-18 10:38 commons-pool-1.3.jar
-rw-r--r-- 1 root root 7574 2006-12-18 10:38 jdk-searcher.jar
-rw-r--r-- 1 root root 153276 2006-12-18 10:38 jdom.jar
-rw-r--r-- 1 root root 94028 2006-12-18 10:38 jmock-SNAPSHOT.jar
-rw-r--r-- 1 root root 154642 2006-12-18 10:38 JNIWrap.jar
-rw-r--r-- 1 root root 121070 2006-12-18 10:38 junit-3.8.1.jar
drwxr-xr-x 2 root root 4096 2006-12-18 10:39 latest
-rw-r--r-- 1 root root 17789 2006-11-14 15:47 launcher.jar
-rw-r--r-- 1 root root 358085 2006-12-18 10:38 log4j-1.2.12.jar
-rw-r--r-- 1 root root 280984 2006-12-18 10:38 mail.jar
-rw-r--r-- 1 root root 106911 2006-12-18 10:38 nanocontainer-1.0-RC-1.jar
-rw-r--r-- 1 root root 9196166 2006-12-18 10:38 openapi.jar
-rw-r--r-- 1 root root 13045 2006-12-18 10:38 patches-impl.jar
-rw-r--r-- 1 root root 2589 2006-12-18 10:38 patches.jar
-rw-r--r-- 1 root root 76958 2006-12-18 10:38 picocontainer-1.1.jar
-rw-r--r-- 1 root root 2725184 2006-12-18 10:38 resources_en.jar
-rw-r--r-- 1 root root 645701 2006-12-18 10:38 resources.jar
-rw-r--r-- 1 root root 9890 2006-12-18 10:38 shaj-0.5.jar
-rw-r--r-- 1 root root 716456 2006-12-18 10:38 testng-5.2-jdk15.jar
-rw-r--r-- 1 root root 413662 2006-12-18 10:38 trove4j.jar
-rw-r--r-- 1 root root 16491 2006-12-18 10:38 utils.jar
-rw-r--r-- 1 root root 610253 2006-12-18 10:38 winpack.jar
-rw-r--r-- 1 root root 116065 2006-12-18 10:38 xmlrpc-2.0.1.jar
-rw-r--r-- 1 root root 24676 2006-12-18 10:38 xpp3_min-1.1.3.4.M.jar
-rw-r--r-- 1 root root 246867 2006-12-18 10:38 xstream-1.1.2.jar
root@ptbuild05:~#

root@ptbuild05:~# ls -l /opt/tc-agent/plugins/
total 44416
drwxr-xr-x 5 root root 4096 2006-12-18 10:39 ant
-rw-r--r-- 1 root root 6729923 2006-12-18 10:39 ant165.jar
drwxr-xr-x 3 root root 4096 2006-12-18 10:39 antPlugin
-rw-r--r-- 1 root root 30441 2006-12-18 10:39 antPlugin.zip
drwxr-xr-x 3 root root 4096 2006-12-18 10:39 coveragePlugin
-rw-r--r-- 1 root root 433252 2006-12-18 10:39 coveragePlugin.zip
drwxr-xr-x 4 root root 4096 2006-12-18 10:39 dotnetPlugin
-rw-r--r-- 1 root root 178730 2006-12-18 10:39 dotnetPlugin.zip
drwxr-xr-x 5 root root 4096 2006-12-18 10:39 idea
-rw-r--r-- 1 root root 34239685 2006-12-18 10:39 idea_dist.jar
drwxr-xr-x 3 root root 4096 2006-12-18 10:39 inspectionPlugin
-rw-r--r-- 1 root root 79870 2006-12-18 10:39 inspectionPlugin.zip
drwxr-xr-x 3 root root 4096 2006-12-18 10:39 iprPlugin
-rw-r--r-- 1 root root 2273850 2006-12-18 10:39 iprPlugin.zip
drwxr-xr-x 6 root root 4096 2006-12-18 10:39 maven-2.1
-rw-r--r-- 1 root root 1299539 2006-12-18 10:39 maven-2.1.jar
drwxr-xr-x 3 root root 4096 2006-12-18 10:39 mavenPlugin
-rw-r--r-- 1 root root 23644 2006-12-18 10:38 mavenPlugin.zip
drwxr-xr-x 2 root root 4096 2006-12-18 10:39 META-INF
drwxr-xr-x 3 root root 4096 2006-12-18 10:39 testNGPlugin
-rw-r--r-- 1 root root 10899 2006-12-18 10:39 testNGPlugin.zip

Could you please give a try to TeamCity 1.2 RC. This exception should not happen in it, but I'd like to make sure that's true.
Please note, 1.2 RC is quite stable.

Crazy thought ...

Ubuntu ships with GCJ as the "java".
I haven't tried, but TeamCity may run in this environment despite the fact that it is unsupported and generally a bit flaky compared with one of the Sun JDKs.

Are you just running with whatever the system default java is, or have you installed a JDK?

Forgot to mention - I did actually read your bit about having installed 1.5.0_05. This doesn't necessarily mean it is the one being used. GCJ might rank higher in /etc/alternatives.
Just a thing to rule out.

OK. Just read your attached teamcity.log. Spanking myself.

Scott, any feedback on this issue?

I will test this out in the next couple of days.

SH