SCCM 2012 R2 - Add Untrusted Forest - 8007052E "The Username or password is incorrect"

Issue:
You try and add a new, untrusted forest into your SCCM 2012 setup but SCCM refuses to accept the credentials of the discovery account account

Error Code: 0x8007052E
Error details: The user name or password is incorrect

Cause:
The user name or password is incorrect..........or is it? Turns out this is a pretty misleading error message. SCCM is basically blaming you for getting the password or username wrong. The root cause, however, is more to do with what you're trying to authenticate against.

Fix:
Enter the name of a domain controller as a prefix to the LDAP lookup. So rather than LDAP://DC=test,DC=local you'd need to enter LDAP://dc01.test.local/DC=test,DC=local