>> I had to change my contributor to a co-author, because when she went to filter, she was given an error message by FormsCentral that told her she had to be a co-author.
I am not able to reproduce your problem. Your shared-users as contributor should be able to filter the responses.
Please share the form to me @ email@example.com as contributor, and I will take a look.
Because our form information is confidential, I will try a few tests and let you know the results.
On the hunch that this was a fluke, I switched everyone on that form to Contributor again and will give them additional instructions to open a personal view for filtering. This way, if the conflict was caused by two people trying to filter at once, we will eliminate that variable.
I will let you know how it goes.