Errors with ogr2ogr and DXF files (ASCII and BIN)

Question

Using OGR, I'm trying to reproject a DXF file. I'm using ogr2ogr, but I get two type of errors depending if I start with a BIN DXF or an ASCII DXF file.

With BIN DXF:

ogr2ogr -s_srs 27492.prj -t_srs 4326.prj myfile_WGS84.dxf myfile_BIN12.dxf

I get this error message:

FAILURE:
Unable to open datasource `myfile_BIN12.dxf' with the following drivers.
[+ the list of installed drivers, included DXF]

With ASCII DXF

ogr2ogr -s_srs 27492.prj -t_srs 4326.prj myfile_WGS84.dxf myfile_ASCII12.dxf

I get this error message:

FAILED: Layer entities already exists, and -append not specified.
        Consider using -append, or -overwrite.
ERROR 1: Terminating translation prematurely after failed
translation of layer entities (use -skipfailures to skip errors)

(effectively, 'entities' does exist, but this the expected situation, right?)

I don't know what I am doing wrong. I tried with different BIN and ASCII versions (R13, R14, 2007, 2010), with the same errors.

Thank you very much in advance.