php errors on frontpage

Hi all

We host a multi-network multi-site instance of wordpress for our students.
On our frontpage, we aggregate all blog entrys of its subsite (something like a blog-planet). This is realized with Diamond MultiSite Widgets. Now, whenever someone vistits our main site, the following php error is logged:

WordPress database error  for query SELECT user_id, meta_key, meta_value FROM wp_usermeta WHERE user_id IN (35) made by require, require_once, include, get_constructor_layout, Constructor_Main->getLayout, include_once, get_constructor_sidebar, Constructor_Main->getSidebar, get_sidebar, locate
_template, load_template, require_once, dynamic_sidebar, call_user_func_array, DiamondBL->widget_endView, DiamondBL->render_output

Any ideas how to fix this?