For version 12.0 you need to install MDAC 2010 from here.
This has to be done on the server where you publish your application.
You need to install the x86 version if the target machine is 32 bit or the x64 version if the target machine is 64 bit and your application is built with configuration Any CPU.
Your connection string is right so this error could be caused by following reason:
This post has detailed info on how to troubleshoot it.