acroread plugin not working

[Sam D]

Code:
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    ~$ firefox

  LoadPlugin: failed to initialize shared library /usr/lib/Adobe/Acrobat7.0/Browser/intellinux/nppdf.so [/usr/lib/Adobe/Acrobat7.0/Browser/intellinux/nppdf.so: undefined symbol: XtCalloc]

  LoadPlugin: failed to initialize shared library /usr/lib/Adobe/Acrobat7.0/Browser/intellinux/nppdf.so [/usr/lib/Adobe/Acrobat7.0/Browser/intellinux/nppdf.so: undefined symbol: XtCalloc]
--------------------




Anybody knows what does that mean ?


-- 
Sam D