Current versions of mojoPortal require ASP.NET 3.5 SP1.
It sounds like you have made your own build from the source code, because the latest version will not build against 2.0 .NET, I'm sorry its not working for you but I do not know any way to help you with an error in that situation because your code is not in a known state. The error itself sounds like a stored procedure is out of sync with data access code and has more or fewer parameters than what the stored procedure expects or you have an error in your version of the code declaring a parameter incorrectly.
As far as the folder url not working, I would go into site settings for the root site, select the child site from the list and check if the folder mapping is still there.
Hope it helps,