Blender could not convert the .blend file to .fbx

Keep getting this error, not sure why. I’m using blender 2.5.
If I export as an FBX it works except animations made in the action editor are lost.
Any ideas?

You tried to import in just blend files?

If you’re using a newer version of blender, you should check the External Tools section, there’s a few posts in there on how to get unity3d to import from newer versions of blender.