First, make sure you are using Pro Tools 6.11 for Windows, the first version of Pro Tools which allows both the ASIO and Wave drivers to be installed at the same time.

Then, make sure to download both the ASIO and Wave driver for 6.11 from their website. It's possible when you did the 6.1 to 6.11 update that the ASIO driver which is automatically installed with 6.1 was left in there and thus is causing conflicts with the 6.11 ASIO or Wave driver. Try installing both the 6.11 ASIO and Wave driver to resolve the problem.