Sometimes when building a unity project you might run into a build error. This error message is logged in the console of unity. Sometimes the message is to long to fit in this window, so it says <message truncated>
to read the full log entry you need to open the unity log files. The file in which this entry is added is called Editor.log.
You can find it on these locations and it can be opened by any text editor:
Mac osx: ~/Library/Logs/Unity/Editor.log
Windows xp: C:\Documents and Settings\username\Local Settings\Application Data_\Unity\Editor\Editor.log
Windows vista/7: C:\Users\username\AppData\Local\Unity\Editor\Editor.log
You can read more about unity log files at unity documentation.