So finally i found what is the problem. if you ever face such kind of problem then execute this command in sql server and see whether your table is connected to any schema apart from dbo. Use this statement to check whether the table is connected to any other schema.
use yourDatabaseName
Then
SELECT * FROM INFORMATION_SCHEMA.TABLES
after that if you find that your table is connected with other schema apart from dbo then use your any statement like this
select * from schemaName.tableName
(eg. my schema name is z3ctjholo and my table name is product_Design)
so my statement would be like this
select * from z3ctjholo.product_Design
what i was doing wrong, i was using two schema names (z3ctjholo.dbo.product_Design).
I hope it will help someone..
Thanks...