Recently we got the below error in one of our SSIS Packages
The packages were working fine in one of the environments and were failing in another.
It was throwing an error in one of the lookup fields that was referring to the alternate key. Here the alternate was defined with 2 fields.
As it turned out in another environment the order of the fields was changed for the alternate key field.
We recreated the alternate key field in the proper order of the attributes to fix this.
Hope it helps..