The portal fields used in the relationship must be stored, indexed fields. A calculation field that refers to a field in a different table is by definition an unstored field so your calcFilter field cannot be used in this relationship.
I'm not sure exactly how you want to use a specified prospect setting and company name setting, but you might try this relationship:
View::Prospect = Company::Prospect AND
View::companyfilter = Company::Name
This allows you to specify 1 or 0 for prospect and then select a company name in the company filter field and your portal will then display all matching values.
If you want to set up a "partial company name match", in FileMaker 10 and older versions, you'll have trouble doing it. It will be much simpler to upgrade to FileMaker 11 so that you can do this with a portal filtering expression instead of trying to implement this in a relationship.
Thanks for the reply,
I upgraded to fm11 and all works fine now