Every now and again the Arduino IDE spits out an error message along the lines of “couldn’t determine program size” or simply fails to compile with no error message at all. The former is evidently harmless, but the latter can be truly annoying.
The cause is described for Macs there as a race condition in the IDE on multi-core processors, with a patch that either partially fixes the problem or pushes it to a less-likely part of the code. That’s true on my system, as the error still occurs occasionally.
How you apply it to Xubuntu 8.10: unzip the file to get Sizer.class, then copy that file to /usr/lib/jvm/java-6-sun-126.96.36.199/jre/lib/. That won’t be the right place for a different Xubuntu or different Java, so use locate rt.jar and plunk it into that directory.
A less dramatic change seems to be setting build.verbose=true and upload.verbose=true in ~/.arduino/preferences.txt.
In my case, both of those changes did bupkis.
This is evidently an error of long standing, as it’s been discussed since about Arduino 11. I’m currently at 15 and it seems that patch will be in the next version of the IDE.