Iam getting error Value Off Track is invalid for this field

EntityQuery query = new EntityQuery();

query.TypeName = "Workitem";

OrderBy orderByName = new OrderBy();

orderByName.FieldName = "Name";

Compare cond1 = new Compare();

cond1.LeftExpression = new FieldExpression() { FieldName = "TrackStatus" };

cond1.Operator = Operator.Equal;

cond1.RightExpression = new ConstantExpression()

{

Value = "Off Track"

};

Compare cond2 = new Compare();

cond2.LeftExpression = new FieldExpression() { FieldName = "TrackStatus" };

cond2.Operator = Operator.Equal;

cond2.RightExpression = new ConstantExpression()

{

Value = "At Risk"

};

query.Where = new Or() { Conditions = new Condition[] { cond1, cond2 } };