I'm not sure what that error means.... You may have to look at your existing links
I would use this command for the dynamic parameter only - don't link it to anything and don't use its fields in the report except for in the parameter. That way it would not be included in the SQL that the report runs and instead will only run for the parameter values.
Yes, you can add parameters to the command. You have to create them IN THE COMMAND EDITOR, not in the report (commands require some additional internal properties in the parameter that are not set up when creating them in the report.) If the parameter is a string value, you'll have to put single-quotes around it when you put it in the query. It will look something like this:
description = '{?Parameter}'
-Dell