Sorry that I reply that late but had not much time to map and test things.
Don't use GEN_OPTIONS, just add fs_basepath, -game and fs_game into each compile step, like cosmo's compile a couple posts up.
Probably this wouldn't change anything. I tried though and it really doesn't change anything. Here is the compile batch file I used based upon cosmo's.
@set PATH2Q3MAP2="C:\Programme\GtkRadiant14\compiler\q3map2.exe"
@set PATH2MAPFILE="C:\Spiele\OpenArena076_dev\baseoa\maps\test.map"
%PATH2Q3MAP2% -v -game ioquake3 -fs_basepath "C:\Spiele\OpenArena076_dev\" -fs_game baseoa -bsp -meta -flares %PATH2MAPFILE%
%PATH2Q3MAP2% -v -game ioquake3 -fs_basepath "C:\Spiele\OpenArena076_dev\" -fs_game baseoa -vis -v %PATH2MAPFILE%
%PATH2Q3MAP2% -v -game ioquake3 -fs_basepath "C:\Spiele\OpenArena076_dev\" -fs_game baseoa -light -fast -dirty -patchshadows -samples 4 -bounce 8 -gamma 2 -compensate 4 %PATH2MAPFILE%
The compile error log looks the same as I posted

.
EDIT: Damn it. The problem was cause by the last slash at parameter -fs_basepath "C:\Spiele\OpenArena076_dev\". After removing this the compile works as desired. Any problem related to sky lightning and wrong texture sized are gone. Sorry for wasting your time.
The working batch file:
@set Q3MAP_PATH="C:\Programme\GtkRadiant14\compiler\q3map2.exe"
@set MAP_PATH="C:\Spiele\OpenArena076_dev\baseoa\maps\%1.map"
@rem @set GEN_OPTIONS=-fs_basepath "C:\Spiele\OpenArena076_dev\" -game baseoa -fs_game baseoa
@set GEN_OPTIONS= -game baseoa -fs_game baseoa -fs_basepath "C:\Spiele\OpenArena076_dev"
%Q3MAP_PATH% %GEN_OPTIONS% -meta -mv 1024 -mi 6144 -v -custinfoparms %MAP_PATH%
%Q3MAP_PATH% %GEN_OPTIONS% -samplesize 4 -custinfoparms %MAP_PATH%
%Q3MAP_PATH% %GENOPTIONS% -vis -custinfoparms %MAP_PATH%
%Q3MAP_PATH% %GEN_OPTIONS% -light -fast -samplesize 4 -samples 2 -filter -patchshadows -dark -external -lightmapsize 256 -custinfoparms %MAP_PATH%