I have now also found a solution that works perfect for me:
Open the registry; Start > Run > regedit

Try to check the registry if you don't have any entry called:
HKEY_LOCAL_MACHINE\SOFTWARE\Lotus\Notes\6.0

if you don't, check the entries under 7.0 and copy them to an entry called 6.0. Values should be the same in both key's (6.0 and 7.0)
Good luck!