Notes mail user is no longer able to open / read HTML mail when opened. Images are broken (red boxes) and error message is presented that says, "Cannot open the web navigator database".
User deleted their perweb.nsf database and/or removed the entry in the location document where its filename is specified.
Recreate the "perweb.nsf" database from the template. If not fixed, also make sure the location document specification of "perweb.nsf" is correct. If that still doesn't work you need to re-compute the location form by performing the following:
Switch the preferred Internet browser to "Notes" and for the retrieve/open option underneath, select "from Notes workstation" and save the location document. Test at this point, and you should find the email(s) can be opened. Now switch it back to the previous setting such as "Notes with Internet Explorer" or "Internet Explorer". It works.