We have been running Jira 1.4.2 in production (Tomcat & Oracle).
I have been testing Jira 2.0 (standalone) - I imported the data from the 1.4.2 database export (I didnt do an upgrade). At some point I noticed that I could not close an issue (it remained open).
On initial investigation, I found an exception being logged when trying to close an issue. On further investigation, I found an exception being logged when a new issue is created in the first place (though the issue appeared to be created successfully).

When I create a new issue, I get a workflow exception - the underlying exception is "java.sql.SQLException: Violation of unique index:" (I will attach the full stacktrace)

I have since done another export from our production database (and imported it again into a 2.0 Jira), and it seems to running fine - though I dont know whether we will again run into this problem.

What further info do you need from me?
(I will have to find out if I can send you the standalone DB - as it might have sensitive info in it...)

-Nick