Due to a regression in SDK Tools r12 and r13 (see Android bug #18444), running any builds with the "Use emulator snapshots" option enabled (which is the default), would likely fail to load in the state you expect. For example the emulator may not be ready for use, and the screen may not be unlocked.
To avoid this, either keep using r11 or earlier, or update to r14 or newer. However, if you update, you will have to manually delete all existing snapshot images and allow this plugin to re-create them.
Similarly, snapshot support is not yet fully functioning in for Android 4.0. An initial snapshot can be created, but subsequently loading from that snapshot will crash the emulator immediately. Earlier Android versions are not affected, i.e. you can still use snapshots with Android 3.2 and earlier.
As a workaround, you can uncheck "Use emulator snapshots" in any jobs where you are seeing problems.