problems after upgrading to 7.4.5

hi all experts

please help me
here's the story...
i an working on a Java based Web Application
which is made up of
Jsp's -tomcat jsp server(3.1.1)
EJB's-Jonas EJBServer (2.4.4)
RDBMS-postgres (7.3.4)
JDK Platform is 1.4.2

the application was working fine with this config since 2 years

then some while ago this app was upgraded to postgres v7.4.5 after which the problem started

Problem 1)     first when i started the jonas server i got an error saying
                    SET AUTOCOMMIT OFF is no longer supported.
Resolution 1): i downloaded pgjdbc2.jar and restarted the JOnas server
                    things looked to work  fine

Problem 2): when i tested the application it was running fine.i was able to add products to
                  the shopping cart and all the things
                  but when i restart the jonas server after some code changes
                  i started getting error in the cart such as
ERR#          EnqCartBean:viewEnqcart:fetchin enqMasterjava.rmi.ServerException: RemoteException occurred in server
thread;nested exception is: 
                   javax.transaction.TransactionRolledbackException: System exception in business method

                  the transaction got rolled back and all products in the cart were lost.
                  i tried by again adding the parts and the application started giving more and more errors

ERR#         CartDetailClient:Cannot create Cart detail: javax.transaction.NotSupportedException: Nested transactions
notsupported 
ERR#          javax.transaction.TransactionRolledbackException: cannot register EntityContext
ERR#          EnqCartBean:addToEnqCartjavax.ejb.DuplicateKeyException: E0000053(even if 53 is not there)

Tries 1  : i tried by changing the newly available jdbc drivers from posgres.org
               1)pg74.216.jdbc2ee.jar
               2)pg74.216.jdbc3.jar and also others
             with these jars there was a strange issue i was able to connect and login to app but the product list
             and all the reporst were  not showing any records(this attempt also failed)
Tries 2 :  i learnt from the postgres site that SET AUTOCOMMIT OFF is not supported in 7.4
            so this might be a problem.so i set that option at postgres console by command SET "AUTOCOMMIT OFF"
            after this also problem is not solved

i am clue less about where actually the problem is it the driver i am using or there is a need to change the EJB code
or
deployment descriptors.i'm new to EJB and also the code is quite old

pls help me.i have given it a real hard fight but no gains.basically where shud i attack

please mail me at

aquajags@yahoo.com
jrao@econify.com

regards
jags