Hi Sivaram,
Keymapping process is improved a lot in the latest patch release.
however, for java heap error, you are left with only one option that is excel based keymapping.
Please refer to the user guide for the same or you can map the object one by one using the keymapping GUI as you were doing before.
Suggestion is to upgrade to the lastest patch of SAP b1 and intercompany both.
Regards,
Agneesh
The Intercompany Team