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 not supported
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(at)yahoo(dot)com
jrao(at)econify(dot)com

regards
jags