In all your webs, change references to topics that moved to the TWiki.TWiki web:
Change topics: TWikiUsers , WebNotify , WebHome
With links to: TWikiPreferences , TWikiVariables , TWikiUsers , TWikiWebsTable , WelcomeGuest
Move your TWikiWebsTable topic to TWiki.TWiki.
Merge your changes to TWikiPreferences into TWiki.TWikiPreferences , then delete Main.TWikiPreferences
In case you customized TWikiRegistration , merge your changes back into TWiki.TWikiRegistration , then delete Main.TWikiRegistration .
In case you have authentication: Change .htaccess to reflect the new location of the TWikiRegistration , i.e. ErrorDocument 401 /cgi-bin/view/TWiki/TWikiRegistration