SSPI cannot be generated when using VPN connection

I am the developer of a time recording tool written in vb.net using odbc. Using this tool from home via vpn (cisco) everything is working for ME and one other person. My collegue could connect too but since she got a new windows installation it is not working anymore. Also all other users in our company cannot connect. They get the error: *`"Cannot generate SSPI context"`*. Only my collegue get the error *`*"the target principal name is incorrect. Cannot generate SSPI context."*`*. Everyone can ping the sql-server and the tool is perfectly working in LAN. The useres can access the file server and use other vb.net programmed tools (all without a sql-server backend though). We use windows authentication for logging into the sql-server. I checked the usernames there everything is ok.