Hibernate 4.1.8 uses the FBClob.length() method when reading Clobs from the database, in the current version of Jaybird the method throws a FBDriverNotCapableException which Hibernate can't handle.

Caused by: org.firebirdsql.jdbc.FBDriverNotCapableException: Not yet implemented.
at org.firebirdsql.jdbc.FBClob.length(FBClob.java:69)
at org.hibernate.type.descriptor.java.DataHelper.extractString(DataHelper.java:278)

JDBC does not require this method to be implemented: http://docs.oracle.com/javase/7/docs/api/java/sql/Clob.html#length() :
SQLFeatureNotSupportedException - if the JDBC driver does not support this method. FBDriverNotCapableException extends SQLFeatureNotSupportedException (in the Java 6 and 7 version of Jaybird).

Maybe there are other drivers out there that do the same, so maybe it is wise to handle the exception generically

More details: http://tracker.firebirdsql.org/browse/JDBC-270