Link Sever Is Not Working

I have a SQL Server 2000 running on win 2003 where there is Linked Sever.
Recently we have upgrade the SQL server 2000 to SQL 2005 and things were fine but suddenly one day things stopped working when I have tested the connection for link server. It failed and gave me this error. What could be the possible error .

The source it is linked is a System DSN which is linking is a remote server running Informix Database. The driver is Informix CLI-2.5 (32 bit). Is it the driver that is the cause of error or what ???


"The test connection to the linked server failed."
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An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)
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Program Location:
at Microsoft.SqlServer.Management.Common.ServerConnec tion.ExecuteNonQuery(String sqlCommand, ExecutionTypes executionType)
at Microsoft.SqlServer.Management.Smo.ExecutionManage r.ExecuteNonQuery(String cmd)
at Microsoft.SqlServer.Management.Smo.LinkedServer.Te stConnection()
at Microsoft.SqlServer.Management.UI.VSIntegration.Ob jectExplorer.LinkedServerConnectionTest.Invoke()
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Cannot initialize the data source object of OLE DB provider "MSDASQL" for linked server "INFORMIX_LIBRARY".
OLE DB provider "MSDASQL" for linked server "INFORMIX_LIBRARY" returned message "[Microsoft][ODBC Driver Manager] Driver's SQLSetConnectAttr failed".
OLE DB provider "MSDASQL" for linked server "INFORMIX_LIBRARY" returned message "[Microsoft][ODBC Driver Manager] Driver's SQLSetConnectAttr failed".
OLE DB provider "MSDASQL" for linked server "INFORMIX_LIBRARY" returned message "[INTERSOLV][ODBC Informix driver][Informix]Unable to load locale categories.". (.Net SqlClient Data Provider)