how can I catch the return messages of the FM?

Hi abap gurus...

i have a problem with standard function module SD_ORDER_CREDIT_RELEASE.

i am using this function module to release salesorders.

it's working fine.

but i need the return messages in tables or export parameters.

for that i did:

1. i create a z function module and inside that i call the SD_ORDER_CREDIT_RELEASE.

2. i debugged it ( to find out from where the return messages came). i didnt find out that.

could you please help me

lakshman