I cannot install Easy Blogging plugin

Dear sir/madam,

I’m trying to install the plugin I have bought (Easy Blogging) on my site http://www.hkznl.nl, but I got a next error message;

Notice: Trying to get property of non-object in /home/mstanic/domains/hkznl.nl/public_html/wp-admin/update.php on line 111 Notice: Trying to get property of non-object in /home/mstanic/domains/hkznl.nl/public_html/wp-admin/update.php on line 111 Notice: Trying to get property of non-object in /home/mstanic/domains/hkznl.nl/public_html/wp-admin/update.php on line 120
Plugin will be installed.
Installation Package not available.
Back to the plugin installation.

When I login to the dashboard of WPMU I see my purchased product.
What am I doing wrong?

Regards,
Mario