Hello,
It looks like upon creation of a group you are trying to set a certain property that has the DN syntax, but the value that you set does not comply with all the requirements for DNs that the property accepts. For example, you can have a Business Rule triggered after creating a group, that can add some objects to a new group, and not all of those objects are from the same forest as the new group itself.
To troubleshoot the issue, first of all, how do you create the groups? Do you create them manually or via import, for example? Do you use the Administration Console or the Web Interface for this purpose? Can you also post here or send to our support e-mail (support[at]adaxes.com) a screenshot of the error that you get?