Last night I found a problematic module... Specifically, it was XML Sitemap, but I do not think it was specific to that module.

The problem? I lost the XML Sitemap menu. I could not access it at all. So I decided to run the update.php code to see whether that would wake it up. Did not work. Then I tried going in the Modules list and disabling the modules. Did not work! Wow! I could not disable these modules!!! How weird...

So I finally decided to go in the database and mark the status as disabled (i.e. 0 instead of 1). That worked and the module was now disabled. I could even uninstall it—well... maybe, at least it appeared in the Uninstall list.

I re-enabled the modules I use and it worked again.

What did happen?!

I'm not 100% sure, but I think that the problem was the throtle. I had several of the XML Sitemap marked as Throtle since I had the Throtle module turned on at some point. But that Throtle module was turned off now... Yet, I was thinking that the Throtling flags may very well still be active. Meaning that the XML sitemap module would be inaccessible because of a missing module, and even just turned off because Drupal core could not know that it should ignore the flags once the Throtle module is turned off (Ooops!)

Just so you know, I had many problems because the Throtle module would arbitrarily turn off modules that are dependencies of others and it would just break the whole site in one way or another. Now why the Throtle got used when I'm still working on the site? Not too sure... we got 5,600 hits on the home page in a couple of days. I just cannot explain those (I do not have access to the Apache logs.) At the time, it took me about 6 months to get that many hits on my Linux Page (this very website http://linux.m2osw.com — today I get about 7,000/mo. though).