This template and similar ones on Wikipedia provide a convenient way to browse a category by letting it start on a particular numeral or letter. An example on this site is http://www.mediawiki.org/wiki/Category:All_extensions.
The template worked for me in MW 1.16, but it stopped doing so in MW 1.17 (for no apparent reason). Manually adding &from=M (for M) to the URL achieves nothing unfortunately.
How do we go about enabling it again?
I worked it out myself. Both here and on Wikipedia, the templates add the string &from= to the page name or URL followed by the initial letter/numeral requested. However, I found that the string which needs to be added is &pagefrom= rather than &from= (if you click on "next 200", that's what it using as well). I can't tell why that should be different on my site - it may be an extension changing the configuration, or it may be that WP and this site are using modified versions of MW 1.17. In any event, I expect that all I need to do now is to correct the template.
Regards,
In my case, this solution was almost immediately followed by database corruption (in the searchindex table to be precise). Hopefully (and probably), it was just an unfortunate case of one problem queuing up for another.