hi bilal,
yes, this has to do with your GGSN : the PDP context is either accepted or refused by the GGSN.
Agha says that the external network is refusing the connection -> in other words, it may indicate that your GGSN is not able to access the Internet. Please check with your GGSN colleagues that your APN are well handled by GGSN, that the firewall on the Gi interface is well configured, etc.
Regards,
pix