Hmm, First I have never used Leto. So I have no Idea what instructions you are following, I can only comment on what does not make since.
First the Toolset/module does not have Bic files. Even if one is imported into the toolset, It will not be able to do anything with the file. The only time a Bic file will be in a module is when it is a saved game( .sav file). If you open up a saved game in the toolset, that has a bic file in it, the bic file gets lost when the module is resaved.
An ERF file is a bunch of files, or just one file, packed into a single file. If the file you are placing into the ERF is a .bic file the toolset just does not know what to do with it.
I assume that you are tring to turn your PC int a NPC then import him into the module. If that is the case open the ERF file you are creating and make sure that the file you are placing into it is not the .bic file.
You can open the ERF file with nwhak.exe or nwexplorer.