CRM 365 getting an error in the c# code using fetchexpression.

Hello All Experts,

i trying to fetch the records from within the crm using fetchxml and fetchexpression.

var fetchExp = new FetchExpression(fetchXML);

var contactEntityCollection = _serviceProxy.RetrieveMultiple(fetchExp); //Error line at compile time.

cannot convert fetchexpression to Microsoft.Xrm.sdk.query.querybase.

Can anyone help me in resolving this issue please.