You can only install the K2 webparts while running sites in 2010 Compatibility mode.

K2's Compatibility Matrix

Hi PetrKazada,

Which version of K2 BP and SF are you running? According to the compatibility matrix the latest K2 Blackpearl which is 4.6.7 is only compatible with SharePoint 2013 Standard and Enterpise. Please have a look at the link below which leads to the Compatibility Matrix. 

http://help.k2.com/blackpearlmatrix.aspx

Kind Regards,

Yannick

Hi all, thank you for replies.

Is there any plan to make the K2 BP compatible also with Sharepoint Foundation 2013? Lot of our customers demand this combination.

You can use the K2 for Sharepoint web parts (that were designed to run with SharePoint 2010) with SharePoint 2013 Foundation as long as your sites are run in 2010 compatibility mode.