Problem with calender import

Hi there,
I am new here and I have a question.
I try to synchronize my calenders with nextcloud. With two calendars there is a problem. It says analyze calender and doesn’t proceed. Can anybody help me please.
BTW, I have some problems with changing the password for using the web-interface. Either it doesn’t work orI can’t login after changing.
I use nextcloudpi on raspberry poi 3b