I know this is an old thread, but a google search sent me here after I experienced a similar problem with my A500 running KS2.05+WB2.1.
The solution is to:
* Install aguide34.lha from aminet.
* Install 2b_mv_os2.lha and 2b_mv_prefs.lha from aminet.
* Navigate to SYS:Utilities and left-click the MultiView icon, then right click and select Icons->Information from the menu. This brings up the Information window.
* The "Tool Types" box is where the MultiView config details are kept. Click "New" and enter "DEFAULT=SYS:Utilities/AmigaGuide" (without quotes) in the box and click "Save".
* MultiView should now correctly display AmigaGuide and text files.
It appears MutliView defaults to using AmigaGuide, but maybe it's looking for a newer version (like paul1981 hinted at) so it fails. By defining DEFAULT to use our installed AmigaGuide, things start to work.
By the way, I was using a fresh install of WB2.1 (from original disks) and it didn't contain AmigaGuide. I had to install it from aminet. That wikipedia article linked above is either incorrect or there are different "versions" of WB2.1 out there.