Really what that message means is that you're using read-ahead and JBoss got an error trying to load all of the entities data at the time the finder was called. It then falls back on the innefficient two-phase load (find identifies the key set and a separate load is issued for each entity effected).
The 'char' is a member of your bean (i mean, do you have a CMP field of type char)? There are some problems with char fields, IIRC. But then why does a regular load work.
What version of JBoss? Assuming 2.4.x, not 3.0, I'll look at the code this evening.
I found the error. seems that Jboss 2.4.x is not able to retieve CMP fields from the database if they are 'char' in the java code. I changed the char to a String. Works perfectly. Also, I tried Jboss 3.0, the char worked there.