The error looks like you have an instance based attribute assigned to the Folder object in the Type and Attribute manager, but you and your users do not have the suffiecient permission or some other problem preventing you from writing to that IBA. "Name" should be an out of the box field, but maybe your admin was experimenting and added "name" as an IBA as well, but then messed something up.
So, it is either a bad IBA that is somehow causing the problem, in which case look in the type and attribute manager. If you find a bad IBA, then removing might need PTC Tech Support help if you are not comfortable with SQL updates or writing java clean up programs.
On the other hand, if it's access control, then you just need new rule(s).
I'd start by going to the project in the domain administrator and giving FULL permission on just the subfolder object to you to see if that helps. If it does, then play with access control until you get what you like.
However, if that doesn't work (and I don't think it will), give FULL control to youself for WTobject in that project in the domain administrator. See if that works. It might. If it does, then you likely have some access problem around IBA tables or something odd, and fixing will depend on where the problem is - more testing will help narrow it down by changing the rules until you find the object that is the problem.
Finally, if FULL control on wtobject is not good, then you have some bad set up in your type and attribute manager like a null pointer, or uninstantiable object referenced by the subfolder class, or who knows. If you aren't a good business admin familiar with the type and attribute management system, then I'd get PTC Tech support to help at that point.
Al
