OK, so I have followed all the below steps, and managed to see the unique participant ID appended to the outgoing millisecond URL at the end of the survey, but once I clicked on the link, the IAT launch page wouldn't open. It said: Page cannot be found. Any idea why this could be happening?
"Another way to do this is to have your participants start in the survey web site, and use whatever method that survey offers for creating a unique identifier for each respondent. When the survey is finished, configure the survey package to forward each participant to the Inquisit launch page address, and to append the respondent's unique id to the url as query parameters. Query parameters are a standard mechanism for sharing data between different web sites, and many survey packages have this capability. Consult the support resources offered by your survey package for instructions on how to forward participants to a url with the subject id as a query parameter.
The following shows an example of a url to an Inquisit experiment with a query parameter at the end of it:
http://research.millisecond.com/sniffles/myexperiment.web?respondentid=134
The url contains a single parameters named "respondentid", the values of which is "134". Inquisit can be configured to handle any parameter name. You will have to configure your survey package to dynamically insert the appropriate id value for each participant.
To configure Inquisit to retrieve the subject id from the query parameter, simply run through the webscript registration wizard. When asked how to generate subject ids, select the "Query Parameter" option and specify the name of the parameter (in this case, the name is "respondentid"). That's it, Inquisit will now extract this subject number from the url and record it in the data file."