MSN has dropped me from their listing for my main keyword...?

Ok, so I've been ranked #11 for a very popular keyword, and today I see that for that keyword I'm not even in the top 1000 results, but I am still in their index. I noticed, that the indexing for my home page is a database error page.

Two days ago I was having a problem so the main page gave a database error, and that's all that was on the page. This is what MSN has just put into their index as of today. Could this be the reason, and I just need to wait for MSNbot to go back and reindex it again?

Also, I used a 301 redirect for index.php to go to www.domain.com. Could this be a potential reason as well? Is it possible that MSN had my index.php ranked well, but for some reason www.domain.com did not rank (canonicalization issue), and now index.php 301 redirects to www.domain.com. Therefore, there is no index.php anymore, so it does not rank anymore for that keyword.

Do either of these explanations make sense?

I guess you answered your own questions. I believe both of them will affect your rankings. Until the next crawl and caching process, make sure everything is ok. I believe your rankings will be back..