I have found that doing research for one thing, will allow you to peel back layers of the onion on other things that are related to what you're researching for and sometimes others that you find by accident. Case in point is MOS Note 554356.1 about the how and why ORIG_SYSTEM_REFERENCE can't be updated, then opposite is MOS Note 1462348.1 which explains TCA API causes for the errors and also how to fix them. What's so great about this last note? It covers R12 API errors that can be encountered for the TCA product!
Hungry for more? Look at bug 9352630 for another way to solve the problem brought up in Note 554356.1 since it doesn't look like Oracle will be solving this anytime soon.