Losing connection in an ESQL/C Applikaction

Hey, I've written an ESQL/C Applikation which is embedded in an C++ Applikation. We are working with Informix OWS 7.22 on Windows NT. My Problem is that I lost the connection in a transaction. I call at the Programm intialisation: EXEC SQL connect to :db_name as :username WITH CONCURRENT TRANSACTION; Looking of the transaction: EXEC SQL set connection :username; EXEC SQL begin work; Transactions select, insert, update... EXEC SQL commit work; In the transaction I get the errormessage: -1803 "Connection does not exist" When I then try to recconnect the Errormessage is: -1802 "Connection in use" Is there anyone who can help me?