Maor, I have a feeling we already saw and fixed this in 3.2 - please check (and solve if not).
This bug is a duplicate of https://bugzilla.redhat.com/854185. We can see that the same exception occurs in the current bug [1] and in BZ854185 [2]: [1] 2013-05-16 17:18:57,003 ERROR [org.ovirt.engine.core.bll.TryBackToSnapshotCommand] (ajp-/127.0.0.1:8702-13) [696ff4a4] Command org.ovirt.engine.core.bll.TryBackToSnapshotCommand throw exception: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 at java.util.ArrayList.rangeCheck(ArrayList.java:604) [rt.jar:1.7.0_09-icedtea] at java.util.ArrayList.get(ArrayList.java:382) [rt.jar:1.7.0_09-icedtea] at org.ovirt.engine.core.bll.BaseImagesCommand.findImageForSameDrive(BaseImagesCommand.java:218) [engine-bll.jar:] [2] 2012-09-04 15:18:28,049 ERROR [org.ovirt.engine.core.bll.TryBackToSnapshotCommand] (ajp-/127.0.0.1:8009-13) [6bd0a119] Command org.ovirt.engine.core.bll.TryBackToSnapshotCommand throw exception: java.lang.IndexOutOfBoundsException: .... org.ovirt.engine.core.bll.BaseImagesCommand.findImageForSameDrive(BaseImagesCommand.java:218) [engine-bll.jar:] Also tried to reproduce it on the upstream and no exception was thrown. *** This bug has been marked as a duplicate of bug 854185 ***