error when comparing two factor variables

I want to create a new variable with a certain value when two other variables: CountryOfOrigin and CountryOfBirth are identical. I use Variable-Conditional Compute-Multiple.

IF

PAIS_NACIM == PAIS_PROC_DEST 

THEN

"País de procedencia"

I always get the following error

n argument: `LugarNacimiento = ifelse(PAIS_NACIM == PAIS_PROC_DEST,

"País de procedencia", NA)`.

Caused by error in `Ops.factor()`:

! level sets of factors are different

Thank you for any comment.