winetricks dotnet11 doesn't yet do
$WINE uninstaller --remove '{E45D8920-A758-4088-B6C6-31DBB276992E}'
as it should. You could try that before 'winetricks dotnet11'.
What app are you trying to install? (And what's a good .net 1.1 test app?)
But dotnet20 installation is currently broken, see
http://bugs.winehq.org/show_bug.cgi?id=30845
