A "DataAccessException: Error occured while retrieving user with id '...'" bug was reported against Mylyn when retrieving an issue from a JIRA 3.12.3 repository that is assigned to a user that does not exist anymore. The repository has crowd integration enabled.

236034: Synchronisation aborts, when entry is retrieved having a user which does not exist on server anymore
https://bugs.eclipse.org/bugs/show_bug.cgi?id=236034

Similar bugs have been filed here:

http://jira.atlassian.com/browse/CWD-202
http://jira.atlassian.com/browse/JRA-12360

Unfortunately the exception is thrown on the server side and there is no good way to recover on the client. Would it be possible to return a null user instead of throwing an exception in the case of a non-existant user?

I don't have a full stack trace since I don't have crowd and can not reproduce the scenario but I believe the SOAP call causing the exception is getIssue().