I just checked with DF 0.44.10 + DFHack 0.44.10-beta1 + LegendsViewer 1.19.08 and everything works fine for me. What OS do you use?
I have the graph issue resolved now. This was caused by lack of Internet Explorer 9. I use Vista x64, and it had IE8, IE9 apparently being optional. I've noticed that LV uses IE files, but at first though it's for internet access only, not as rendering engine. Later I saw I can see source of the displayed information, so copied it to HTML file, and displayed in my old Firefox, and then realised what's the issue. Then I downloaded IE9 and installed (I also applied the last Vista security update, which was for IE9 specifically), and this resolved the problem. As a side note, now my IE does crash when launched separately, but that's OK, as long as Legend Viewer works.
This seems to be a DFHack and or DF issue. I just tried it with exactly your world name "region4410b_Wetsalve_LEGENDS_250" and get the same result. Maybe the name is too long or a special case when there are more than one underscore characters in it. I don't know.
LegendsViewer has nothing to do with exporting the files but it expects the files to have this naming scheme:
<worldname>-<year>-<month>-<day>-legends.xml
<worldname>-<year>-<month>-<day>-world_history.txt
<worldname>-<year>-<month>-<day>-world_map.bmp
<worldname>-<year>-<month>-<day>-world_sites_and_pops.txt
<worldname>-<year>-<month>-<day>-legends_plus.xml
<worldname>-world_gen_param.txt
Thank you for answer. The naming issue is minor, and apparently on the DFHacks side anyway. I renamed the world_gen_param too, just in case it is used (is it?).