I had a similiar problem on my website.
This is a solution from customer support:
You can not schedule a web page to be run at a specified time. The task scheduler can only handle files that are executable, such as cgi files or files with a .exe extension. In order to use the scheduler to run a task at a predefined time you will need to compile the file as either a cgi file or an executable file and then upload it into the cgi bin folder.