Unable to query changed date in Product Studio through code

Hi,

I am querying Product studio and unable to get result set when queried on Changed Date,Opened Date,Resolved Date

- <Query>
- <Expression Column="Changed Date" Operator="equals">
  <DateTime>1/23/2015</DateTime> 
  </Expression>
  </Query>

What's wrong with the above query, can anyone help me out.

And also besides equals operator, other operators are throwing errors while executing query(DatastorelistItem.Execute).