I'm not sure what your problem is. An importat part of that stack trace is the part where it tells you what it found that it couldn't match. Another important piece of informatnion is the type of the parameter.
You can compare an entity to an entity valued parameter. You can compare a field to a parameter of the same type, with one exception. In EJB-QL, you are not allowed to compare dependent value classes (any class other then the simple primitive wrappers, dates, and entities); this restriction has been removed in JBossQL