InternalError in UserAccessControlProvider

[Ian Boston]

Hi,
JR 1.5.6

I am getting an "Internal Error" from the UserAccessControlProvider  
traced with a debugger to line
UserAccessControlProvider .java:506 where the code says
             } catch (RepositoryException e) {
                    // should never get here
                    log.error("Internal error ", e.getMessage());
                }

On inspection the error is
javax.jcr.InvalidItemStateException: c86bf464-509e-4e8a-808a- 
fd729cef0be9: the item does not exist anymore

Users are being created and deleted from the security workspace when  
this is happening.

Although the comment says it should not happen, it does, regularly.

Is it anything to be concerned about ?

Thanks
Ian