undefined index errors? plugin: events+

Hi,
I am working with the newest version of wordpress and buddypress and am finding many plugins to generate errors about undefined indexes. Why would this be the case? I have not altered any code. I even went to the extreme of starting all over again, erasing my database and wordpress files but am still having problems (with many different plugins). For example, I am currently trying to install events+ and when I set up the plugin and try to save I am redirected to a white screen with a bunch of error messages. When i try to create an event, there are also error messages generated. Could you help me with this? Thanks, Natalie

I have copied a list of the current errors when working in events+ below:
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Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848 Notice: Object of class WP_Post could not be converted to int in /customers/1/6/1/knallhatten.se/httpd.www/intranet/wp-includes/functions.php on line 2848