Unable to start wptdriver.exe


I have configured the Private instance by following the steps given http://andydavies.me/blog/2012/09/18/how-to-create-an-all-in-one-webpagetest-private-instance/

When I click on the wptdriver.exe in start up folder, i have received the below error

‘The application has failed to start because wpthook.dll was not found. Re-installing the application may fix this problem’.

Could some one please suggest me the steps to resolve this issue.