Facing issues when TFS is Updated from TFS 2013 update 5 to TFS 2015.2.1.

Hi

we are using the Microsoft.TeamFoundation.WorkItemTracking.Client.Query to query the tfs

var acceptanceCollection = new TfsTeamProjectCollection(new Uri("http://tfs/defaultcollection"));
var _workItemStoreAcceptance = acceptanceCollection.GetService<WorkItemStore>();
var accQuery = new Query(_workItemStoreAcceptance, queryText, parameter);

where queryText contains the WIQL query and parameter contains the "asofsate" datetime value

When we invoke the API (last line of the code)we are getting an exception "The string was not recognized as a valid DateTime. There is an unknown word starting at index 0."

Thanks in advance

Girish