Cannot delete a parameter or assign a value at run time

[forumhelp]

Hi Everyone,

I am working on crystal reports XI and there is a parameter which I can neither delete nor I can pass a value in this parameter from visual basic at run time. I want to use the parameter and the same parameter is being passed to other sub reports. While changing the datasource location if I set it to Null then while running the report, it prompts to enter a value in the parameter and if I enter if manually then it is working fine.
Any idea why is it happening?