I'm not sure if this is an issue with the Derby driver or Hibernate. I do know that it surfaced after upgrading Hibernate to 3.5.6 Final from 3.3.2. Final.

Any suggestions as to what might cause this?

Caused by: java.sql.SQLDataException: An attempt was made to get a data value of type 'java.sql.Types 4' from a data value of type 'java.io.Reader'.
at org.apache.derby.client.am.SQLExceptionFactory40.getSQLException(Unknown Source)
at org.apache.derby.client.am.SqlException.getSQLException(Unknown Source)
at org.apache.derby.client.am.ResultSet.getCharacterStream(Unknown Source)
at org.apache.derby.client.am.ResultSet.getCharacterStream(Unknown Source)
at org.apache.commons.dbcp.DelegatingResultSet.getCharacterStream(DelegatingResultSet.java:299)
at org.hibernate.type.AbstractLongStringType.get(AbstractLongStringType.java:54)
at org.hibernate.type.NullableType.nullSafeGet(NullableType.java:186)
at org.hibernate.type.NullableType.nullSafeGet(NullableType.java:212)
at org.hibernate.loader.criteria.CriteriaLoader.getResultColumnOrRow(CriteriaLoader.java:148)
at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:647)
at org.hibernate.loader.Loader.doQuery(Loader.java:745)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:270)
at org.hibernate.loader.Loader.doList(Loader.java:2449)
... 42 more
Caused by: org.apache.derby.client.am.ColumnTypeConversionException: An attempt was made to get a data value of type 'java.sql.Types 4' from a data value of type 'java.io.Reader'.
at org.apache.derby.client.am.Cursor.getCharacterStream(Unknown Source)
... 53 more