Maybe you have/had other versions of Blender installed too, anyway this usually means that your system does not recognize it as the launching app. for the .blend files (looks like Unity uses the System specs for this). I would select a .blend file at the finder, open the info window for it and change the default opening app. there again. Then set it as default for any .blend file.
What happens if you double click a .blend file, does it open Blender? If it doesn’t, then you need to associate the .blend file with Blender 2.49b. Right click the .blend file, select “open with” then select “other” and finally click the “always open with” box.
Can you export to .fbx from inside Blender? If you cannot, then you don´t have the exporter correctly installed, and so unity cannot use it. My last idea so far…
A-a-a, when i first install Blender (on blender3d.org only .zip archive), all scripts they were installed, and models can import to Unity… I three weeks ago worked in Unity and in me everything worked. Several days ceased ago to work, I reinstall blender and scripts and there were not… I relaunch scripts (blender.app/resources/.blender/scripts/)… scripts before this worked beatifully. Unity not import…
If you drag down the info panel, what is displayed in the scripts path setting? I’ve set mine to a folder where I keep all my blender scripts. If you’re loading an external script to export to .FBX, perhaps this is the problem?
Hmmm… could be the problem. The “.blend” path is a hidden path and perhaps when Unity launches Blender it’s not seeing the scripts within? I don’t know, just a thought.