If you try to start up your K2 Service after installing K2 5.2 Fix Pack 8, you may run into this issue:

"Error","System","2001","ServerStartError","SourceCode.Hosting.Server.Runtime.HostServerEngine.StartHostServer","2001 Error Starting Host Server: System.Data.SqlClient.SqlException (0x80131904): Incorrect syntax near 'INDEX'. If this is intended as a part of a table hint, A WITH keyword and parenthesis are now required. See SQL Server Books Online for proper syntax.

In K2 Five, only SQL 2014 and onwards is supported: https://help.k2.com/k2compatibilitysupportmatrix#SQLServer

The reason the issue occurs is because the server has SQL 2012 or lower installed. We advise you to install SQL 2014 when installing K2 Five.

However, if you have already run into the issue, please install the latest K2 5.2 Fix Pack to rectify the issue: https://help.k2.com/kb002760

KB article for reference.