The version of Crystal that you're using has been out of support for over 10 years. It was never designed to work with newer versions of databases, including MySQL. Also, when dealing with long text fields, it may only display 256 characters. If you were using a newer version of Crystal I would recommend that you either write a Command to generate the data for your report or use SQL Expressions to cast the memo fields to VarChars.
You cannot control the casting with a parameter. For the version of Crystal that you have, you'll have to edit the SQL that was created by Crystal so that the cast is done in the SQL.
Did you write the application that you're using the reports in? If so, what language and, if it's .NET, what version of Visual Studio was used?
-Dell