I got the same error even though I already had RB installed. Haven't 
had a chance to debug it though.

>I'm getting this error when I try to install BrowseUnit v. 3 in a fresh
>3.7a-5763 image: "MessageNotUnderstood: BrowseUnit class>>browse".   The
>problem seems to be in the SAR's postscript:
>	StringHolder new acceptContents: (self memberNamed:
>'install/readme.txt') contents;
>		openLabel: 'README'.
>	^ BrowseUnit browse
>
>I didn't see any dependencies listed for the BrowseUnit package, so I
>haven't installed the RefactoringBrowser or Whisker, etc..  
>
>Thanks,
>Brent


-- 
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Source code in files. How quaint. -- Kent Beck