That is because you've isolated the calendar in a seperate database from the rest of your site. Since you're using a content manager, it (the CMS) assumes that you have everything in 1 database and only establishes the database connection once at the begining of the script. Since the calendar is encapsulated in itself, it creates its own connection to its database. If the two connections aren't the same, then the CMS will try to use the connection that the calendar established... This is proved by this little error message...
Table 'pfreak_calendar.wp_posts' doesn't exist
pfreak_calendar is your calendar's database, and the CMS is trying to find wp_posts in that database.
To fix it, just move (or recreate) the calendar's table in your CMS' database.
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