Enrique got an hard to track error (without a clear error message) in import after he changed the reference of C_BPartner_ID from search to table.
See https://groups.google.com/d/msg/idempiere/_hYxW9My3go/6gEi-nKCU3kJ for a deeper explanation.
The error shows up when importing a "table" column with a validation but no reference table set. This is for example the case for C_BPartner in C_Order table.
This must be solved in actual code - please reopen if this is still reproducible