javax.ejb.IlleglStateException is a unchecked exception. (So you dont have to declare it in a throws clause explicitly). This exception is thrown when you call a method of the EJBContext interface where you dont have access to the method you called. Eg. Calling getRollBackOnly() from a BMT MDB.
If you need further clarification and u r in reach of HFEJB read the exceptions chapter which will make it clear to u.