Hi, Alan,
I don't use parameter fields in Crystal, so this is a total guess on my part - you might need to include the CrystalDecisions.Shared namespace.
If I can give you my two cents on this - when I prompt the user for information that will appear on a Crystal report, I usually define columns in the dataset that's associated with a report. Often times I'll have a table called RptHeader that drives header data for a report (company name, report title, name of user running the report, etc.) - if the report also contains data from user prompts, I'll include columns for that data. Just something to think about.
Kevin