System.ConfigurationErrorsException: Unrecognized attribute 'useDefaultSecurityLabel'. Note that attribute names are case-sensitive. (C:Program Files (x86)K2 blackpearlHost ServerBinK2HostServer.exe.Config line 359)
It looks like there may be an issue with the XML in your K2HostServer.exe.config file. To verify all attributes are correct (i.e. comments are closed out with "-->", spelling is correct, etc), please go to C:Program Files (x86)K2 blackpearlHost ServerBinK2HostServer.exe.Config, ensuring that you first backup the config file before making any changes. Once backed up, open this file and browse to line 359 (this is where the error is getting thrown). If you open this file with NotePad++ you should see line numbers which may assist with troubleshooting.
If you don't notice any glaring issues within the config file, please let me know.
It is likely there is an extra node in the xml in the K2HostServer.exe.config file. Maybe you can try removing the 'useDefaultSecurityLabel' attribute in line 359 and see if it that resolves the error.