missing actions, close, resolve etc. + related error in logfile

Even though a user (or group) has rights to set a issue to closed/resolved etc, the option to do this doesn't appear.

In the catalina.out there're a lot of messages like these :

[ERROR] AbstractWorkflow - -Error checking available actions <java.lang.NullPointerException>java.lang.NullPointerException
at com.opensymphony.workflow.spi.ofbiz.OfbizWorkflowStore.findEntry(OfbizWorkflowStore.java:166)
at com.opensymphony.workflow.AbstractWorkflow.getAvailableActions(AbstractWorkflow.java:106)
at com.atlassian.jira.web.action.issue.ViewIssue.loadAvailableActions(ViewIssue.java:412)
at com.atlassian.jira.web.action.issue.ViewIssue.getAvailableActions(ViewIssue.java:391)
at sun.reflect.GeneratedMethodAccessor95.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)

I've upgraded from 2.5.3 to 2.6.1 , some issues I can now close, but the problem still persists on others.