The sgcWebSockets Trial already includes all Indy files required, because is the Enterprise version, which uses a custom Indy version. There is no need to install the indy 10 version (this is only required for Standard or Professional packages).
The error is raised because the linker find sgcIdTCPClient unit which is different from the included inside the trial/libD7 folder.
Just delete the Indy version installed (and all dcu, bpl...) and try again with only the Delphi 7 trial. It should work.
Thank you, - but it dident help me .. I still suffer this problem in Delphi 7 :
[Warning] sgcIdStackWindows.pas(1822): Return value of function 'TIdSocketListWindows.GetItem' might be undefined
[Warning] sgcIdIOHandler.pas(2630): Return value of function 'TIdIOHandler.WriteFile' might be undefined
[Fatal Error] sgcWebSocketsD7.dpk(225): Unit sgcWebSocket_Client was compiled with a different version of sgcIdTCPClient.TIdTCPClientCustom.SetReadTimeout
I installed Indy10 (downloaded from this/your site), and the indy-components are available on Delphi 7's palette, but still, I cannot install scgWebSockets.
I have searched Google a lot, but I find no clue as to what the solution is ...