This market needs at least a source (e.g., The Economist) and a timeframe (e.g., between the beginning of 2007 and the end of 2010).

There doesn’t appear to be any reports in the popular press about significant failures amongst African MFI’s even with the current credit market conditions. News, in fact is neutral to positive. For example:

http://www.time.com/time/business/article/0,8599,1863443,00.html

African press (at least accessible via google search) does not decry any widespread failures. For example:

http://www.africanexecutive.com/modules/magazine/articles.php?article=3609

Microfinance Insights, an industry journal cites funding difficulties but no report of widespread failures either in their November/December 2008 review of Africa.

https://www.microfinanceinsights.com/articles_new.asp?member=nonmembers&id=347
https://www.microfinanceinsights.com/comments_tab.asp?id=29

Nor does anything I could find on the Microfinance Information Exchange indicate failure issues including comparing their 2007 and 2008 Top 100 MFI lists.

http://www.themix.org/default.aspx

Of course, those who are interested in attracting more capital to the sector might try to sweep failure under the rug but one would think a high failure rate would have hit the popular press while funding issues would have led for more strident appeals to various interested parties.

While I could find no definitive source for an answer, based on the above, I’m guessing the absolute failure rate is below 25%. Presumably those that failed “due to lack of investment capital” would be even less as the absolute failure rate would include failures due to “poor lending decisions/excessive losses” and “inefficient cost structures” among other things.