Disappointing timeline problem, I guess:P

After I put an animated softbody into my scene, I no longer can change materials on objects. When I do it, Blender doesn`t save the changes and after I re-load the scene, objects have their original materials instead of the new ones.

I`ve read in a LightWave manual that it is necessary to create keyfremaes for every change. Now, when I change a material,  also make new keyframe [Link and Materials panel: Delete, then in the materials tab, Add new>Data browse, choosing one, and clicking "Create new keyframe" or sth like that in the timeline window]. Now, the new material is persisting when I re-load the scene, but the renderer ignores it and renders the object whose material has been changed as if it had no material at all.

Blender 2.42a, rendering frame 150, softbody is baked [doesn`t matter, I guess:P].

Any help appreciated! I`m just about finishing this project and these problems stopped me for several weeks [madly busy with my exams;)].