After I noticed that my accounts were not synchronized I reinstalled Davdroid but I cannot add my account. In the link you can find the logs. Note that even if the response from the server is 403 I am sure that the username and password were correct. I checked them more times and I have no problems with other softwares. Note also that my password contains symbols and I would not that some of them are not well handled by Davdroid. I am thinking about the at sign, the colon or the backslash.