Having seen this issue several times on various forums, thought it would be a good idea to blog about it. In some cases, Reporting Services parameters with default values wouldn’t default and so you would have to manually select the values in the parameters. Obviously, this defeats the purpose of setting default values as you are required to manually select the values when running the report.
So what is the reason behind this issue? There could be 2 possible reasons based on my experience:
1. You have NULL or blank values in the dataset you have used to populate the parameter. There are two ways to fix this:
b. In the parameter properties, select the check boxes “Allow blank value” and “Allow null value” as shown in the figure below: