Are you seeing any output from the build engine process (jbe)?

If not, try specifying the java executable (not javaw) on the command line.
By default jbe uses the system default JDK or JRE, but that can be problematic (e.g. the javac task will only work with a JDK, not a JRE).
It's best to use the same JDK that ships with the RTC client.

You can also add -verbose to get more details.

For example:
jbe -vm {path_to_rtc_client}/jazz/client/eclipse/jdk/bin/java -repository {repoURL} -userId {buildUser} -pass {password} -engineId {engineId} -verbose