or alternatively, try using "quotation" marks around the win style path statment.
The php.ini and/or httpd.conf file chokes on invalid paths...
if its unquoted it expects a UNIX style path statement, if quoted it takes it as a literal string.
But be consistent... I have made all my references to win paths w/ "x:\path" and works. Especially if they have spaces like
"C:\Program Files\Apache Group\Apache\htdocs"
vs.
C:\Program Files\Apache Group\Apache\htdocs
Would suppose that the truncated 8.3 style might work unquoted, but never tried it, ...just a guess.