Glaucia,
for certain interpolation methods, e.g., Kriging, input data are not allowed which contain the same data point more than once. The data have to be preprocessed to be able to use them for interpolation.
For simple ASCII triplet files (*.trp), there is a tool coming with FEFLOW for deleting double values (trp_deldouble in the tools subdirectory). For using the FEFLOW datatools, please see tools.pdf in the /doc directory on the FEFLOW DVD.
Peter