Fields in the hibernate mapping files declared as type "string_max" should be truncated to the parameterized length. The mapping files do this parameterization with a "length" attribute on the property element. It looks like this (from ActionLog.hbm.xml):

<property name="exception"
type="string_max"
column="EXCEPTION_"
length="4000" />

4000 also happens to be what StringMax will use if it can't find or parse its parameterization. We needed to shorten some fields to fit jBpm into MS SQL Server. When we shortened the length, we noticed that the parameter was being ignored, causing jdbc to blow chunks. org.jbpm.db.hibernate.StringMax.setParameterValues() always gets a null passed in for it's parameters with this setup. To get it to work , we changed it to

<property name="exception" column="EXCEPTION_">
<type name="string_max">
<param name="length">1000</param>
</type>
</property>