Bamboo should look for the BUILD FAILED message along with the BUILD SUCCESSFUL message to determine build out come.

.........
17-Jun-2008 17:07:08       [exec] > rem signed c:\bamboo_home\some.dll 
17-Jun-2008 17:07:09       [exec]      [echo] Signing c:\bamboo_home\some.dll... 
17-Jun-2008 17:07:10       [exec] BUILD SUCCESSFUL 
17-Jun-2008 17:07:10       [exec] Total time: 1 second 
......
17-Jun-2008 17:07:12       [exec] Unable to load c:\bamboo_home\some.exe 
17-Jun-2008 17:07:12       [exec] error 2 
17-Jun-2008 17:07:12       [exec]         File size         Ratio      Format      Name 
17-Jun-2008 17:07:12       [exec]    --------------------   ------   -----------   ----------- 
17-Jun-2008 17:07:12       [exec] upx: c:\bamboo_home\some.exe: FileNotFoundException: c:\bamboo_home\some.exe 
17-Jun-2008 17:07:12       [exec] Packed 0 files. 
17-Jun-2008 17:07:12       [exec] > rem signing problem ---> c:\bamboo_home\some.exe not exists! 
17-Jun-2008 17:07:12       [exec]  
17-Jun-2008 17:07:12       [exec] Build log was saved at "file://c:\some.log" 
17-Jun-2008 17:07:12       [exec] SOMEPLAN - 2 error(s), 0 warning(s) 
17-Jun-2008 17:07:12   
17-Jun-2008 17:07:13       [exec] ---------------------- Done ---------------------- 
17-Jun-2008 17:07:13   
17-Jun-2008 17:07:13       [exec]     Rebuild All: 0 succeeded, 14 failed, 11 skipped 
17-Jun-2008 17:07:13       [exec]  
17-Jun-2008 17:07:13   
17-Jun-2008 17:07:14       [exec] Result: 1 
17-Jun-2008 17:07:14   
17-Jun-2008 17:07:14  BUILD FAILED 
17-Jun-2008 17:07:14  C:\bamboo_home\Products\some.xml:175: The following error occurred while executing this line: 
17-Jun-2008 17:07:14  C:\bamboo_home\some.xml:76: Compile error code is: 1 
17-Jun-2008 17:07:14   
17-Jun-2008 17:07:14  Total time: 3 minutes 2 seconds 
17-Jun-2008 17:07:14  Build process for 'SOME-PLAN Main' returned with return code = 0 
17-Jun-2008 17:07:14  Running post build plugin 'Clover Results Collector' 
17-Jun-2008 17:07:14  Running post build plugin 'Artifact Copier' 
17-Jun-2008 17:07:14  Finalising the build... 
17-Jun-2008 17:07:14  Stopping timer. 
17-Jun-2008 17:07:14  Build SOME-PLAN-27 completed. 
17-Jun-2008 17:07:14  Running post build plugin on server 'Clover Delta Calculator'