[ solved ] Contact Owner - must be same in Accounts

[joebordes]

in one task of "Update related records" you can only set fields from one module, thus the "Duplicate Modules not allowed" message, that is correct

I replicated your setup, with one workflow and two update related tasks, one for contacts and the other for documents. It worked as expected

Activate full debug and reproduce the error, you probably have some SQL error that will give you a clue of what is happening