Did you try acct_mgr-0.3 or better: latest development code of acct_mgr-0.4dev aka trunk yet?
But I suspect there's no issue with AcctMgr at all. You want to use tracd with HTTP Basic Auth, but manage the htdigest file with AcctMgr, right? Make sure, that tracd process is running with a suitable UID, so you have r/w access to that file. You didn't talk about that by now. It seems that you continue to fail with that in your configuration - nothing that AcctMgr could be blamed for. If you're sure, that you'll be able to write to the file from tracd, post your [account-manager] configuration here, please.
Login is yet a different topic. For tracd with HTTP Basic Auth you need to follow t:wiki:TracStandalone#UsingAuthentication. Make sure to not enable AcctMgr's login form.
Btw, what is HttpAuthPlugin (you listed trachttpauth) meant to be fore? It's not needed for normal login as mentioned in the wiki docs, and I think you have more, than you need, or you don't know exactly what to do, so you risk interfering plugin actions. Try to build you setup step-by-step. Activating multiple plugins while having issues is a bad idea - just sort out each one on it's own, ok?
