Software Applications Programming Errors and solutions.

I am getting following SQL Error on running of Enterprise portal ,sharepoint site Could you advice solution on this error. Unknown SQL Exception 10054 occured. Additional error information from SQL Server is included below. A transport-level error has occurred when sending the request to the server. (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by the remote host.) Possible solution: An error has occurred while establishing a connection to the server. When connecting to SQL Serve and this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: TCP Provider, error: 0 - An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full.)