ORA-02298: cannot validate while enabling constraints after impdp

Hi,

 I am using Oracle 10.2.0.5 on Oracle Linux 5.7 as my Production environment and Oracle 11.2.0.4 on Oracle 6.4 for UAT environment.

 My effort is to export data from Production and Import it into UAT and enable all constraints.

 This is my export script on PROD:

expdp directory=DEBIX dumpfile=prod_jboss_data.dmp \
logfile=prod_jboss_data.log content=data_only \
SCHEMAS=JBOSS JOB_NAME=JBOSSEXP flashback_scn=2526790643

 This is my impdp script on UAT:

impdp directory=DATAPUMP dumpfile=prod_jboss_data.dmp \
logfile=prod_jboss_data.log content=data_only schemas=JBOSS

 After a successful import into the JBOSS schema, I am trying to enable all constraints and it fails with error ORA-02298: cannot validate  on some tables.