On Sun, Aug 29, 2010 at 4:27 PM, Hans-Georg Michna <hans-georg@michna.com> wrote:
gpsbabel -w -r -t -i gdb -f C:/Dokumente und
Einstellungen/HG/Eigene Dateien/GPS/Tracks/Mobile
phone/TEMP/test_from_mapsource.gdb -o gpx -F "C:/Dokumente und
Einstellungen/HG/Eigene Dateien/GPS/Tracks/Mobile
GPX cannot open '"C:/Dokumente und Einstellungen/HG/Eigene
Dateien/GPS/Tracks/Mobile phone/TEMP/test_from_mapsource.gpx"'
for write. Error was 'Invalid argument'.

"Can't open for write" probably means it has nothing to do with the contents of the file.   Probably.   It could mean something like you're trying to write t_f_m.gpx into a directory that doesn't exist or something.   More on that in a moment...
Things are getting even more strange now. If I change the file
paths and then try to repeat the operation, I get a log in the
textbox that indicates some earlier path, not the path I
entered. I append a screenshot directly after clicking on the
"Apply" button.

I think we had another report from someone that there was some weirdness if you mixed the <browse> button and manually futzing with the filenames in the dialog.  (This was something that was originally disallowed, but I enabled it late in the beta - and letting people futz with path names lets them do things like try to write files into non-existing directories)   There may be something to that, but I wasn't able to repro it from the original report.

Of course, software most always happens to work the way developers drive it...it's the stuff we never think to try that hoses us up. :-)   So if you can find the recipe to break it, I'll try to make it work better.