After installation of the latest QB buildagent (5.1.30) on Mac machine with "Yosemite Mac OS X (10.10)" on it, agent wasn't able to start and failed with next error:
...
wrapper | Launching a JVM...
wrapper | JVM exited while loading the application.
jvm 5 | Error: This Java instance does not support a 32-bit JVM.
jvm 5 | Please install the desired version.
wrapper | There were 5 failed launches in a row, each lasting less than 300 seconds. Giving up.
wrapper | There may be a configuration problem: please check the logs.

Quick search on PMEase forum showed that it is known issue:
* Forum: http://forum.pmease.com/viewtopic.php?f=1&t=2959
* Issue Tracker: http://track.pmease.com/browse/QB-1858

Though, previous time it affected machines with "Mavericks Mac OS X (10.9)". After DEBUG level for buildagent was enabled, it gave a bit more information:
...
wrapper | Launching a JVM...
wrapper | Java Command Line:
wrapper | Command[0] : /System/Library/Frameworks/JavaVM.framework/Versions/A/Commands/java
wrapper | Command[1] : -d32
...

Very strange that it identifies machine as "-d32", though it is 64-bit.

PS. Commenting out "wrapper.java.additional.auto_bits=TRUE" line in "wrapper.conf" helped to bypass the problem