I installed the latest (SDM 2.5) on to my 1803, and when ever I try to load the web interface (ip http secure-server) I get 404 not found (it attempts to load home_aux.shtml)
I verified that home.tar is present on my flash, but if I do a archive tar /table on it I get a "error parsing" at the top before it lists all the files.
I read on some other forum that it could be a possible bug in IOS but seeings as I don't have a service contract... (cisco should make the base version for your model router available at the very least, but that's another story)
SDM works if installed on a desktop machine also, indicating that it's not a problem with my actual settings.
I'm running 12.4(17) Enterprise IP feature set