Hi,
Yesterday i downloaded Blender 2.55 but when i imports the object in unity it was an error who says that blender could not convert the .blend file to an FBX file and that i need blender 2.45 or higher to direct import blender files
A bit of searching around here or on Unity Answers will illuminate for you that any .blends made with a post-2.49 version won’t work directly. You can manually export a .fbx, but don’t expect everything to carry over properly.