Missing font in book file

Question

I've been getting this missing font message when I open a book file:
The "Arial Black" Font is not available.
  "Arial Black Heavy" will be used in this session.
Why are there font references in the book file (see .mif excerpt below)?
Why am I getting this message when Arial Black is installed, and Arial Black Heavy is not?
<Pgf
  <PgfTag `GroupTitlesIX'>
  <PgfUseNextTag No>
  <PgfNextTag `'>
  <PgfAlignment LeftRight>
  <PgfFIndent  0.0">
  <PgfLIndent  0.0">
  <PgfRIndent  0.0">
  <PgfFIndentRelative No>
  <PgfFIndentOffset  0.0">
  <PgfTopSeparator `'>
  <PgfTopSepAtIndent No>
  <PgfTopSepOffset  0.0">
  <PgfBotSeparator `'>
  <PgfBotSepAtIndent No>
  <PgfBotSepOffset  0.0">
  <PgfPlacement Anywhere>
  <PgfPlacementStyle Normal>
  <PgfRunInDefaultPunct `. '>
  <PgfSpBefore  3.0 pt>
  <PgfSpAfter  3.0 pt>
  <PgfWithPrev No>
  <PgfWithNext Yes>
  <PgfBlockSize 1>
  <PgfFont
   <FTag `'>
   <FFamily `Arial Black'>
   <FVar `Regular'>
   <FWeight `Regular'>
   <FAngle `Regular'>
   <FEncoding `FrameRoman'>
   <FSize  10.0 pt>
   <FUnderlining FNoUnderlining>
   <FOverline No>
   <FStrike No>
   <FChangeBar No>
   <FOutline No>
   <FShadow No>
   <FPairKern No>
   <FTsume No>
   <FCase FAsTyped>
   <FPosition FNormal>
   <FDX  0.0%>
   <FDY  0.0%>
   <FDW  0.0%>
   <FStretch  100.0%>
   <FLanguage USEnglish>
   <FLocked No>
   <FSeparation 5>
   <FColor `Headings'>
  > # end of PgfFont
  <PgfLineSpacing Fixed>
  <PgfLeading  2.0 pt>
  <PgfAutoNum No>
  <PgfNumTabs 0>
  <PgfHyphenate Yes>
  <HyphenMaxLines 2>
  <HyphenMinPrefix 2>
  <HyphenMinSuffix 2>
  <HyphenMinWord 5>
  <PgfLetterSpace No>
  <PgfMinWordSpace 75>
  <PgfOptWordSpace 100>
  <PgfMaxWordSpace 125>
  <PgfMinJRomanLetterSpace 0>
  <PgfOptJRomanLetterSpace 25>
  <PgfMaxJRomanLetterSpace 50>
  <PgfMinJLetterSpace 0>
  <PgfOptJLetterSpace 0>
  <PgfMaxJLetterSpace 10>
  <PgfYakumonoType Floating>
  <PgfAcrobatLevel 0>
  <PgfPDFStructureLevel 1>
  <PgfLanguage USEnglish>
  <PgfCellAlignment Top>
  <PgfCellMargins  0.0 pt 0.0 pt 0.0 pt 0.0 pt>
  <PgfCellLMarginFixed No>
  <PgfCellTMarginFixed No>
  <PgfCellRMarginFixed No>
  <PgfCellBMarginFixed No>
  <PgfLocked No>
> # end of Pgf

Answer 1

You might want to read through these threads:
http://forums.adobe.com/message/1890146#1890146
http://forums.adobe.com/message/1871457#1871457
Check out the referenced MS Hotfix.