SoapUI fails to recognize JDBC drivers.

One of our SoapUI projects contains hte following Groovy script

import groovy.sql.Sql  

// Skip groovy script if DB manipulations are not enabled
def isDBManipulationEnabled = context.expand( '${#Project#IS_DB_MANIPULATION_ENABLED}' )   
if (!isDBManipulationEnabled.equals("true")) return;

def url = context.expand( '${#Project#DB_URL}' )   
def driver = context.expand( '${#Project#DB_DRIVER_CLASS_NAME}' )   
def user = context.expand( '${#Project#DB_USER}' )   
def password = context.expand( '${#Project#DB_PASSWORD}' )   

def MSG_EMPTY_ACTIVATION_KEY = "Empty activation key!"
def MSG_RECORD_NOT_FOUND = "Record not found!"


def activationKey = context.expand( '${CreateB2BContractDOI#Response#//cm30:CreateContractOutput[1]/cm30:CreateContractOutputContractChoice[1]/dom30:B2BContract[1]/dom30:ContractActivation[1]/dom30:activationKey[1]}' )

assert (activationKey!=""):MSG_EMPTY_ACTIVATION_KEY
if ( (null != url) && (null != driver) && (null != user) && (null != password) )   
{   
 try {   
  connection = Sql.newInstance(url, user, password, driver)   
  context.setProperty("dbConn", connection)   
  } 
 catch (Exception e) {   
  log.error "Could not establish connection to the database. "+url+" : "+user+" : " +password+" : "+e.getMessage()   
  assert 1==2 
 }   
} 

which works nicely in SoapUI 3.0.1 but miserably fails in 4.0.1 with "No suitable driver found for jdbc:oracle:thin:@127.0.0.1:1521:ORCL".
The (same) ojdbc6.jar and ora18n.jar are located in bin/ext subdirectories of both soapui-4.0.1 and soapui-3.0.1.

Regards,
Oleksandr