<p>I am working with Cognos8 Report Studio. In my report there are two date prompts: <code>START date</code> and <code>END date</code>. Users can select two different dates or make them both the same date. But the report has valid data only for the last business date of each month. For example, if Jan 31 is Sunday, valid data is available only for Jan 29 which is Friday (the last business day of the month).</p>

<p>Can I have a customized "Date Prompt" where I can disable all other dates except the last business day of each month? Users should be able to select only month-end dates and no other dates?</p>

You can run Rational Robot from the command line, so you should be able to set up a scheduled task to run a .BAT file to do this for you. The command is something like:
[path to Rational Robot]\rtrobo [script file] /user "user name" /project [project file] /play /build "build name" /nolog /close
The Robot documentation will have other arguments you can pass in, depending on your situation.
If a simple scheduled task doesn't work, then you can try setting up a STAF (
http://staf.sourceforge.net/index.php
) environment and create a job to run this.
Good luck :)