problem starting older version 11.1

Hi, I installed the last version of mendeley desktop and then uninstalled it because my computer at work is using office 2003. I then downloaded and installed an older version (11.1). I think it is installed correctly, but I cannot register myself, because when I enter my email and password I got an error message (Incorrect email o password). The thing is that I have no problem signing in online with these email and password. So for now I cannot use mendeley and I need it very soon! Thanks for helping! Annick