For all these year I've been using .NET framework this is first encrypted exception that I get. Here is what I get from quick search
If you are getting the error “Internal .Net Framework Data Provider error 6″ and you are using SQL Server 2005 with database mirroring know that its a bug in the SQL managed client code.
Check out KB article 944099 for more info.
At the time of writing this post the only solution for this problem is a private hot fix that you need to obtain from Microsoft.
The links around the web for the Hotfix Request Web Submission form seems to be broken. I’ve contacted Microsoft and got this replacement link.
Use this link to contact Microsoft, state that you require the hotfix for KB article 944099 and submit the form. You will be contacted shortly by a Microsoft representative that will give you the download details or request further information to better understand your needs.