Hi Sangeetha,
You probably have that assembly cached, so make sure that you go to path C:\Windows\assembly and uninstall the assembly there, then restart BizTalk Host application service.
The next step you do is, in your BizTalk project in Visual Studio, go to Project Properties, click on the Configuration Manager button and change your Active Solution Configuration from Development to Deployment (or vice versa), and make sure that you specify the correct Server and Application Name that you are deploying the artifacts too. Hit Ok to save the changes, rebuild your project and try to deploy it again.
See if the above steps will work for you.
Daniel.