i've builded a custom proj.4 library, tested it by command line (proj and cs2cs) and with postgres/postgis. All works fine.
Now i'm trying to make the same with Qgis 2.2.0. I've replaced the original proj.dll, cs2sc.exe, geod.exe, nad2bin.exe, proj.exe with my customs, in my /OSGeo4W/bin folder.
in Qgis: "settings/custom CRS" + "Add new CRS" in the "parameters" i've copied the same string as for other tests as '+proj=mercxx +ellps=intl +units=m +datum=WGS84 +no_defs' (without quotes)
in 'name' field i've wrote...almost everthing my keyboard can write... even the default 'new CSR' the result is always the same when i hit "OK" : "the proj4 definition of 'mercxx' is not valid.