Error migrating issues?

Migrating from a workflow scheme, back to no workflow scheme (ie default JIRA workflow).

System has no extra statuses.

Workflow migrating from has just Open/In Progress/Closed. Jira default workflow not altered.

Exception:

2004-09-30 08:42:21,984 ERROR [webwork.dispatcher.ServletDispatcher] Could not execute action
java.lang.IllegalArgumentException
at com.atlassian.jira.workflow.AbstractJiraWorkflow.getLinkedStep(AbstractJiraWorkflow.java:169)
at com.atlassian.jira.workflow.OSWorkflowManager.migrateIssueToWorkflow(OSWorkflowManager.java:282)
at com.atlassian.jira.web.action.admin.workflow.WorkflowMigrationManager.migrate(WorkflowMigrationManager.java:150)
at com.atlassian.jira.web.action.admin.workflow.scheme.SelectProjectWorkflowSchemeStep2.doExecute(SelectProjectWorkflowSchemeStep2.java:63)
at webwork.action.ActionSupport.execute(ActionSupport.java:151)
at com.atlassian.jira.action.JiraActionSupport.execute(JiraActionSupport.java:49)
at webwork.dispatcher.GenericDispatcher.executeAction(GenericDispatcher.java:131)
at com.atlassian.jira.web.dispatcher.JiraServletDispatcher.service(JiraServletDispatcher.java:186)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.caucho.server.http.FilterChainServlet.doFilter(FilterChainServlet.java:96)
at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:129)
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:61)
at com.atlassian.jira.web.filters.SitemeshExcludePathFilter.doFilter(SitemeshExcludePathFilter.java:36)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.atlassian.seraph.filter.SecurityFilter.doFilter(SecurityFilter.java:168)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.atlassian.seraph.filter.LoginFilter.doFilter(LoginFilter.java:181)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.atlassian.util.profiling.filters.ProfilingFilter.doFilter(ProfilingFilter.java:132)
at com.atlassian.jira.web.filters.ProfilingAndErrorFilter.doFilter(ProfilingAndErrorFilter.java:25)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.atlassian.jira.web.filters.ActionCleanupDelayFilter.doFilter(ActionCleanupDelayFilter.java:37)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.atlassian.johnson.filters.JohnsonFilter.doFilter(JohnsonFilter.java:91)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.atlassian.jira.web.filters.gzip.GzipFilter.doFilter(GzipFilter.java:72)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.atlassian.core.filters.AbstractEncodingFilter.doFilter(AbstractEncodingFilter.java:36)
at com.caucho.server.http.FilterChainFilter.doFilter(FilterChainFilter.java:88)
at com.caucho.server.http.Invocation.service(Invocation.java:315)
at com.caucho.server.http.CacheInvocation.service(CacheInvocation.java:135)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:246)
at com.caucho.server.http.HttpRequest.handleConnection(HttpRequest.java:164)
at com.caucho.server.TcpConnection.run(TcpConnection.java:139)
at java.lang.Thread.run(Thread.java:534)