Prior to replacing the chaincase gasket I had this issue come up.
Instead of meshing, the lobes of the inner & outer parts of the shock absorber were facing & bearing on each other, compressing the spring.
I couldn't move the parts by hand & had to loosen the spring off considerably before I could get them to mesh properly. The outer retaining nut had been done up dead tight, no problems there. Is this indicative of any problems? I hadn't noticed anything before I took the bike off the road for work.