http://bugs.winehq.org/show_bug.cgi?id=14798
--- Comment #26 from Juan Lang juan_lang@yahoo.com 2011-06-30 11:46:11 CDT --- (In reply to comment #25) warn:chain:CRYPT_KeyUsageValid keyCertSign not asserted on a CA cert
What happens if you change line 1775 of chain.c (in dlls/crypt32) to "ret = TRUE;" instead? That's the line right below the warning you see here.