I tried to install new programs on my laptop but this was refused saying also that "The installer detects that a client already exists that can be modified only by an adminstrator".
Concluding that the adminstrator is me (is that right!?) I went to the user accounts page and tried to open/change this account. But I couldn'open this page neither in order to put it off or on; it simply doesn't react. The funny thing is that I can't uninstall the non working windows installer in order to replace it by a working one.
One detail: there are some programs which I can still uninstall. In the windows programs list the header says remove/change
in that case while in the cases where the installer doesn't work the header only says remove