This is a similar situation to the question asked by WeirdFishes in 2011. I'm working on cross-forest migration, with one domain per forest. A test user has been migrated to the target domain (Windows 2008) but cannot access resources now in the source domain (Windows 2003). I have a two-way forest trust setup. Using the test user in the target domain, I can access resources in the source domain where all users have permissions, but a folder where the test user account in the source domain has specific permission cannot be accessed.
I've confirmed that the test user account in the target domain has the correct SID history.
Can you help?