I turned on the old server and checked it's connect.ini for the correct instance and db name. With that info I tracked down the correct set of folders, with someone from capita support telling me that I only have to copy over the last folder in the path, which is the db name, so I copied that over again incase something had previously gone wrong with the copy. So if the structure is D:\DOCSTORAGE\SERVERNAME\INSTANCENAME\DBNAME\, apparently the only folder you have to copy over from the old server after doing a fresh install on a new server, would be DBNAME. So I did that again and ran the dmconfig again, which apparently isn't really necessary also, since that has all been setup when I installed document server, still wouldn't work. I then ran an office detect and repair on the clients and it started to work on them! Still not working on the server (I'm gussing since that only has word and excel viewers installed although didn't someone say that it should work with just viewers?) but who cares. So it's sorted at one school. So for that particular error (relating to classid's) running the office repair fixed it. Still can't really figure out why though, must be something in office or sims, that relates particularly to the other, and has the old servername, instance name, docstorage location, etc, in it's settings...?
As you said the original / old server had a strange location, i think that the files you've copied to new server are not the real ones, or there is still an error in the pathname. If the old server is still available, fire it up and test reports still work, then check where they are pointing. Copy over the docstorage folder from old server again, you'll know if you're getting the real one, if you've ever used it much, as the size will be quite sizeable. Ours is nearly 3GB now i think. If possible only take over the final folder, above the one with the aa,a0,b1 etc. Put that in the new server at a preconfigured location and rename it to match the databasename if required.